aboutsummaryrefslogblamecommitdiffstats
path: root/library/jsonld/jsonld.php
blob: d3e64e58fae39a9d3e8fb6451eddae1cc2d6b1e1 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760
4761
4762
4763
4764
4765
4766
4767
4768
4769
4770
4771
4772
4773
4774
4775
4776
4777
4778
4779
4780
4781
4782
4783
4784
4785
4786
4787
4788
4789
4790
4791
4792
4793
4794
4795
4796
4797
4798
4799
4800
4801
4802
4803
4804
4805
4806
4807
4808
4809
4810
4811
4812
4813
4814
4815
4816
4817
4818
4819
4820
4821
4822
4823
4824
4825
4826
4827
4828
4829
4830
4831
4832
4833
4834
4835
4836
4837
4838
4839
4840
4841
4842
4843
4844
4845
4846
4847
4848
4849
4850
4851
4852
4853
4854
4855
4856
4857
4858
4859
4860
4861
4862
4863
4864
4865
4866
4867
4868
4869
4870
4871
4872
4873
4874
4875
4876
4877
4878
4879
4880
4881
4882
4883
4884
4885
4886
4887
4888
4889
4890
4891
4892
4893
4894
4895
4896
4897
4898
4899
4900
4901
4902
4903
4904
4905
4906
4907
4908
4909
4910
4911
4912
4913
4914
4915
4916
4917
4918
4919
4920
4921
4922
4923
4924
4925
4926
4927
4928
4929
4930
4931
4932
4933
4934
4935
4936
4937
4938
4939
4940
4941
4942
4943
4944
4945
4946
4947
4948
4949
4950
4951
4952
4953
4954
4955
4956
4957
4958
4959
4960
4961
4962
4963
4964
4965
4966
4967
4968
4969
4970
4971
4972
4973
4974
4975
4976
4977
4978
4979
4980
4981
4982
4983
4984
4985
4986
4987
4988
4989
4990
4991
4992
4993
4994
4995
4996
4997
4998
4999
5000
5001
5002
5003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
5022
5023
5024
5025
5026
5027
5028
5029
5030
5031
5032
5033
5034
5035
5036
5037
5038
5039
5040
5041
5042
5043
5044
5045
5046
5047
5048
5049
5050
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
5076
5077
5078
5079
5080
5081
5082
5083
5084
5085
5086
5087
5088
5089
5090
5091
5092
5093
5094
5095
5096
5097
5098
5099
5100
5101
5102
5103
5104
5105
5106
5107
5108
5109
5110
5111
5112
5113
5114
5115
5116
5117
5118
5119
5120
5121
5122
5123
5124
5125
5126
5127
5128
5129
5130
5131
5132
5133
5134
5135
5136
5137
5138
5139
5140
5141
5142
5143
5144
5145
5146
5147
5148
5149
5150
5151
5152
5153
5154
5155
5156
5157
5158
5159
5160
5161
5162
5163
5164
5165
5166
5167
5168
5169
5170
5171
5172
5173
5174
5175
5176
5177
5178
5179
5180
5181
5182
5183
5184
5185
5186
5187
5188
5189
5190
5191
5192
5193
5194
5195
5196
5197
5198
5199
5200
5201
5202
5203
5204
5205
5206
5207
5208
5209
5210
5211
5212
5213
5214
5215
5216
5217
5218
5219
5220
5221
5222
5223
5224
5225
5226
5227
5228
5229
5230
5231
5232
5233
5234
5235
5236
5237
5238
5239
5240
5241
5242
5243
5244
5245
5246
5247
5248
5249
5250
5251
5252
5253
5254
5255
5256
5257
5258
5259
5260
5261
5262
5263
5264
5265
5266
5267
5268
5269
5270
5271
5272
5273
5274
5275
5276
5277
5278
5279
5280
5281
5282
5283
5284
5285
5286
5287
5288
5289
5290
5291
5292
5293
5294
5295
5296
5297
5298
5299
5300
5301
5302
5303
5304
5305
5306
5307
5308
5309
5310
5311
5312
5313
5314
5315
5316
5317
5318
5319
5320
5321
5322
5323
5324
5325
5326
5327
5328
5329
5330
5331
5332
5333
5334
5335
5336
5337
5338
5339
5340
5341
5342
5343
5344
5345
5346
5347
5348
5349
5350
5351
5352
5353
5354
5355
5356
5357
5358
5359
5360
5361
5362
5363
5364
5365
5366
5367
5368
5369
5370
5371
5372
5373
5374
5375
5376
5377
5378
5379
5380
5381
5382
5383
5384
5385
5386
5387
5388
5389
5390
5391
5392
5393
5394
5395
5396
5397
5398
5399
5400
5401
5402
5403
5404
5405
5406
5407
5408
5409
5410
5411
5412
5413
5414
5415
5416
5417
5418
5419
5420
5421
5422
5423
5424
5425
5426
5427
5428
5429
5430
5431
5432
5433
5434
5435
5436
5437
5438
5439
5440
5441
5442
5443
5444
5445
5446
5447
5448
5449
5450
5451
5452
5453
5454
5455
5456
5457
5458
5459
5460
5461
5462
5463
5464
5465
5466
5467
5468
5469
5470
5471
5472
5473
5474
5475
5476
5477
5478
5479
5480
5481
5482
5483
5484
5485
5486
5487
5488
5489
5490
5491
5492
5493
5494
5495
5496
5497
5498
5499
5500
5501
5502
5503
5504
5505
5506
5507
5508
5509
5510
5511
5512
5513
5514
5515
5516
5517
5518
5519
5520
5521
5522
5523
5524
5525
5526
5527
5528
5529
5530
5531
5532
5533
5534
5535
5536
5537
5538
5539
5540
5541
5542
5543
5544
5545
5546
5547
5548
5549
5550
5551
5552
5553
5554
5555
5556
5557
5558
5559
5560
5561
5562
5563
5564
5565
5566
5567
5568
5569
5570
5571
5572
5573
5574
5575
5576
5577
5578
5579
5580
5581
5582
5583
5584
5585
5586
5587
5588
5589
5590
5591
5592
5593
5594
5595
5596
5597
5598
5599
5600
5601
5602
5603
5604
5605
5606
5607
5608
5609
5610
5611
5612
5613
5614
5615
5616
5617
5618
5619
5620
5621
5622
5623
5624
5625
5626
5627
5628
5629
5630
5631
5632
5633
5634
5635
5636
5637
5638
5639
5640
5641
5642
5643
5644
5645
5646
5647
5648
5649
5650
5651
5652
5653
5654
5655
5656
5657
5658
5659
5660
5661
5662
5663
5664
5665
5666
5667
5668
5669
5670
5671
5672
5673
5674
5675
5676
5677
5678
5679
5680
5681
5682
5683
5684
5685
5686
5687
5688
5689
5690
5691
5692
5693
5694
5695
5696
5697
5698
5699
5700
5701
5702
5703
5704
5705
5706
5707
5708
5709
5710
5711
5712
5713
5714
5715
5716
5717
5718
5719
5720
5721
5722
5723
5724
5725
5726
5727
5728
5729
5730
5731
5732
5733
5734
5735
5736
5737
5738
5739
5740
5741
5742
5743
5744
5745
5746
5747
5748
5749
5750
5751
5752
5753
5754
5755
5756
5757
5758
5759
5760
5761
5762
5763
5764
5765
5766
5767
5768
5769
5770
5771
5772
5773
5774
5775
5776
5777
5778
5779
5780
5781
5782
5783
5784
5785
5786
5787
5788
5789
5790
5791
5792
5793
5794
5795
5796
5797
5798
5799
5800
5801
5802
5803
5804
5805
5806
5807


































































































































































































































































































































































































































































                                                                                                                            
                                                                    










































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                                      
                                                                   

















                                                                              

                              



























                                                                             
                                        

















































































                                                                              
                                 


























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                               





                     

































                                                                            
 



                   
 






























































                                                                             




               

















































































                                                                             




                 



















































                                                                      
<?php
/**
 * PHP implementation of the JSON-LD API.
 * Version: 0.4.8-dev
 *
 * @author Dave Longley
 *
 * BSD 3-Clause License
 * Copyright (c) 2011-2014 Digital Bazaar, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *
 * Neither the name of the Digital Bazaar, Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * Performs JSON-LD compaction.
 *
 * @param mixed $input the JSON-LD object to compact.
 * @param mixed $ctx the context to compact with.
 * @param assoc [$options] options to use:
 *          [base] the base IRI to use.
 *          [graph] true to always output a top-level graph (default: false).
 *          [documentLoader(url)] the document loader.
 *
 * @return mixed the compacted JSON-LD output.
 */
function jsonld_compact($input, $ctx, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->compact($input, $ctx, $options);
}

/**
 * Performs JSON-LD expansion.
 *
 * @param mixed $input the JSON-LD object to expand.
 * @param assoc[$options] the options to use:
 *          [base] the base IRI to use.
 *          [documentLoader(url)] the document loader.
 *
 * @return array the expanded JSON-LD output.
 */
function jsonld_expand($input, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->expand($input, $options);
}

/**
 * Performs JSON-LD flattening.
 *
 * @param mixed $input the JSON-LD to flatten.
 * @param mixed $ctx the context to use to compact the flattened output, or
 *          null.
 * @param [options] the options to use:
 *          [base] the base IRI to use.
 *          [documentLoader(url)] the document loader.
 *
 * @return mixed the flattened JSON-LD output.
 */
function jsonld_flatten($input, $ctx, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->flatten($input, $ctx, $options);
}

/**
 * Performs JSON-LD framing.
 *
 * @param mixed $input the JSON-LD object to frame.
 * @param stdClass $frame the JSON-LD frame to use.
 * @param assoc [$options] the framing options.
 *          [base] the base IRI to use.
 *          [embed] default @embed flag (default: true).
 *          [explicit] default @explicit flag (default: false).
 *          [requireAll] default @requireAll flag (default: true).
 *          [omitDefault] default @omitDefault flag (default: false).
 *          [documentLoader(url)] the document loader.
 *
 * @return stdClass the framed JSON-LD output.
 */
function jsonld_frame($input, $frame, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->frame($input, $frame, $options);
}

/**
 * **Experimental**
 *
 * Links a JSON-LD document's nodes in memory.
 *
 * @param mixed $input the JSON-LD document to link.
 * @param mixed $ctx the JSON-LD context to apply or null.
 * @param assoc [$options] the options to use:
 *          [base] the base IRI to use.
 *          [expandContext] a context to expand with.
 *          [documentLoader(url)] the document loader.
 *
 * @return the linked JSON-LD output.
 */
function jsonld_link($input, $ctx, $options) {
  // API matches running frame with a wildcard frame and embed: '@link'
  // get arguments
  $frame = new stdClass();
  if($ctx) {
    $frame->{'@context'} = $ctx;
  }
  $frame->{'@embed'} = '@link';
  return jsonld_frame($input, $frame, $options);
};

/**
 * Performs RDF dataset normalization on the given input. The input is
 * JSON-LD unless the 'inputFormat' option is used. The output is an RDF
 * dataset unless the 'format' option is used.
 *
 * @param mixed $input the JSON-LD object to normalize.
 * @param assoc [$options] the options to use:
 *          [base] the base IRI to use.
 *          [intputFormat] the format if input is not JSON-LD:
 *            'application/nquads' for N-Quads.
 *          [format] the format if output is a string:
 *            'application/nquads' for N-Quads.
 *          [documentLoader(url)] the document loader.
 *
 * @return mixed the normalized output.
 */
function jsonld_normalize($input, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->normalize($input, $options);
}

/**
 * Converts an RDF dataset to JSON-LD.
 *
 * @param mixed $input a serialized string of RDF in a format specified
 *          by the format option or an RDF dataset to convert.
 * @param assoc [$options] the options to use:
 *          [format] the format if input not an array:
 *            'application/nquads' for N-Quads (default).
 *          [useRdfType] true to use rdf:type, false to use @type
 *            (default: false).
 *          [useNativeTypes] true to convert XSD types into native types
 *            (boolean, integer, double), false not to (default: false).
 *
 * @return array the JSON-LD output.
 */
function jsonld_from_rdf($input, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->fromRDF($input, $options);
}

/**
 * Outputs the RDF dataset found in the given JSON-LD object.
 *
 * @param mixed $input the JSON-LD object.
 * @param assoc [$options] the options to use:
 *          [base] the base IRI to use.
 *          [format] the format to use to output a string:
 *            'application/nquads' for N-Quads.
 *          [produceGeneralizedRdf] true to output generalized RDF, false
 *            to produce only standard RDF (default: false).
 *          [documentLoader(url)] the document loader.
 *
 * @return mixed the resulting RDF dataset (or a serialization of it).
 */
function jsonld_to_rdf($input, $options=array()) {
  $p = new JsonLdProcessor();
  return $p->toRDF($input, $options);
}

/**
 * JSON-encodes (with unescaped slashes) the given stdClass or array.
 *
 * @param mixed $input the native PHP stdClass or array which will be
 *          converted to JSON by json_encode().
 * @param int $options the options to use.
 *          [JSON_PRETTY_PRINT] pretty print.
 * @param int $depth the maximum depth to use.
 *
 * @return the encoded JSON data.
 */
function jsonld_encode($input, $options=0, $depth=512) {
  // newer PHP has a flag to avoid escaped '/'
  if(defined('JSON_UNESCAPED_SLASHES')) {
     return json_encode($input, JSON_UNESCAPED_SLASHES | $options, $depth);
  }
  // use a simple string replacement of '\/' to '/'.
  return str_replace('\\/', '/', json_encode($input, $options, $depth));
}

/**
 * Decodes a serialized JSON-LD object.
 *
 * @param string $input the JSON-LD input.
 *
 * @return mixed the resolved JSON-LD object, null on error.
 */
function jsonld_decode($input) {
  return json_decode($input);
}

/**
 * Parses a link header. The results will be key'd by the value of "rel".
 *
 * Link: <http://json-ld.org/contexts/person.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"
 *
 * Parses as: {
 *   'http://www.w3.org/ns/json-ld#context': {
 *     target: http://json-ld.org/contexts/person.jsonld,
 *     type: 'application/ld+json'
 *   }
 * }
 *
 * If there is more than one "rel" with the same IRI, then entries in the
 * resulting map for that "rel" will be arrays of objects, otherwise they will
 * be single objects.
 *
 * @param string $header the link header to parse.
 *
 * @return assoc the parsed result.
 */
function jsonld_parse_link_header($header) {
  $rval = array();
  // split on unbracketed/unquoted commas
  if(!preg_match_all(
    '/(?:<[^>]*?>|"[^"]*?"|[^,])+/', $header, $entries, PREG_SET_ORDER)) {
    return $rval;
  }
  $r_link_header = '/\s*<([^>]*?)>\s*(?:;\s*(.*))?/';
  foreach($entries as $entry) {
    if(!preg_match($r_link_header, $entry[0], $match)) {
      continue;
    }
    $result = (object)array('target' => $match[1]);
    $params = $match[2];
    $r_params = '/(.*?)=(?:(?:"([^"]*?)")|([^"]*?))\s*(?:(?:;\s*)|$)/';
    preg_match_all($r_params, $params, $matches, PREG_SET_ORDER);
    foreach($matches as $match) {
      $result->{$match[1]} = $match[2] ?: $match[3];
    }
    $rel = property_exists($result, 'rel') ? $result->rel : '';
    if(!isset($rval[$rel])) {
      $rval[$rel] = $result;
    } else if(is_array($rval[$rel])) {
      $rval[$rel][] = $result;
    } else {
      $rval[$rel] = array($rval[$rel], $result);
    }
  }
  return $rval;
}

/**
 * Relabels all blank nodes in the given JSON-LD input.
 *
 * @param mixed input the JSON-LD input.
 */
function jsonld_relabel_blank_nodes($input) {
  $p = new JsonLdProcessor();
  return $p->_labelBlankNodes(new UniqueNamer('_:b'), $input);
}

/** JSON-LD shared in-memory cache. */
global $jsonld_cache;
$jsonld_cache = new stdClass();

/** The default active context cache. */
$jsonld_cache->activeCtx = new ActiveContextCache();

/** Stores the default JSON-LD document loader. */
global $jsonld_default_load_document;
$jsonld_default_load_document = 'jsonld_default_document_loader';

/**
 * Sets the default JSON-LD document loader.
 *
 * @param callable load_document(url) the document loader.
 */
function jsonld_set_document_loader($load_document) {
  global $jsonld_default_load_document;
  $jsonld_default_load_document = $load_document;
}

/**
 * Retrieves JSON-LD at the given URL.
 *
 * @param string $url the URL to retrieve.
 *
 * @return the JSON-LD.
 */
function jsonld_get_url($url) {
  global $jsonld_default_load_document;
  if($jsonld_default_load_document !== null) {
    $document_loader = $jsonld_default_load_document;
  } else {
    $document_loader = 'jsonld_default_document_loader';
  }

  $remote_doc = call_user_func($document_loader, $url);
  if($remote_doc) {
    return $remote_doc->document;
  }
  return null;
}

/**
 * The default implementation to retrieve JSON-LD at the given URL.
 *
 * @param string $url the URL to to retrieve.
 *
 * @return stdClass the RemoteDocument object.
 */
function jsonld_default_document_loader($url) {
  $doc = (object)array(
    'contextUrl' => null, 'document' => null, 'documentUrl' => $url);
  $redirects = array();

  $opts = array(
    'http' => array(
      'method' => 'GET',
      'header' =>
        "Accept: application/ld+json\r\n"),
    /* Note: Use jsonld_default_secure_document_loader for security. */
    'ssl' => array(
      'verify_peer' => false,
      'allow_self_signed' => true)
  );

  $context = stream_context_create($opts);
  $content_type = null;
  stream_context_set_params($context, array('notification' =>
    function($notification_code, $severity, $message) use (
      &$redirects, &$content_type) {
      switch($notification_code) {
      case STREAM_NOTIFY_REDIRECTED:
        $redirects[] = $message;
        break;
      case STREAM_NOTIFY_MIME_TYPE_IS:
        $content_type = $message;
        break;
      };
    }));
  $result = @file_get_contents($url, false, $context);
  if($result === false) {
    throw new JsonLdException(
      'Could not retrieve a JSON-LD document from the URL: ' . $url,
      'jsonld.LoadDocumentError', 'loading document failed');
  }
  $link_header = array();
  foreach($http_response_header as $header) {
    if(strpos($header, 'link') === 0) {
      $value = explode(': ', $header);
      if(count($value) > 1) {
        $link_header[] = $value[1];
      }
    }
  }
  $link_header = jsonld_parse_link_header(join(',', $link_header));
  if(isset($link_header['http://www.w3.org/ns/json-ld#context'])) {
    $link_header = $link_header['http://www.w3.org/ns/json-ld#context'];
  } else {
    $link_header = null;
  }
  if($link_header && $content_type !== 'application/ld+json') {
    // only 1 related link header permitted
    if(is_array($link_header)) {
      throw new JsonLdException(
        'URL could not be dereferenced, it has more than one ' .
        'associated HTTP Link Header.', 'jsonld.LoadDocumentError',
        'multiple context link headers', array('url' => $url));
    }
    $doc->{'contextUrl'} = $link_header->target;
  }

  // update document url based on redirects
  $redirs = count($redirects);
  if($redirs > 0) {
    $url = $redirects[$redirs - 1];
  }
  $doc->document = $result;
  $doc->documentUrl = $url;
  return $doc;
}

/**
 * The default implementation to retrieve JSON-LD at the given secure URL.
 *
 * @param string $url the secure URL to to retrieve.
 *
 * @return stdClass the RemoteDocument object.
 */
function jsonld_default_secure_document_loader($url) {
  if(strpos($url, 'https') !== 0) {
    throw new JsonLdException(
      "Could not GET url: '$url'; 'https' is required.",
      'jsonld.LoadDocumentError', 'loading document failed');
  }

  $doc = (object)array(
    'contextUrl' => null, 'document' => null, 'documentUrl' => $url);
  $redirects = array();

  // default JSON-LD https GET implementation
  $opts = array(
    'http' => array(
      'method' => 'GET',
      'header' =>
        "Accept: application/ld+json\r\n"),
    'ssl' => array(
      'verify_peer' => true,
      'allow_self_signed' => false,
      'cafile' => '/etc/ssl/certs/ca-certificates.crt'));
  $context = stream_context_create($opts);
  $content_type = null;
  stream_context_set_params($context, array('notification' =>
    function($notification_code, $severity, $message) use (
      &$redirects, &$content_type) {
      switch($notification_code) {
      case STREAM_NOTIFY_REDIRECTED:
        $redirects[] = $message;
        break;
      case STREAM_NOTIFY_MIME_TYPE_IS:
        $content_type = $message;
        break;
      };
    }));
  $result = @file_get_contents($url, false, $context);
  if($result === false) {
    throw new JsonLdException(
      'Could not retrieve a JSON-LD document from the URL: ' . $url,
      'jsonld.LoadDocumentError', 'loading document failed');
  }
  $link_header = array();
  foreach($http_response_header as $header) {
    if(strpos($header, 'link') === 0) {
      $value = explode(': ', $header);
      if(count($value) > 1) {
        $link_header[] = $value[1];
      }
    }
  }
  $link_header = jsonld_parse_link_header(join(',', $link_header));
  if(isset($link_header['http://www.w3.org/ns/json-ld#context'])) {
    $link_header = $link_header['http://www.w3.org/ns/json-ld#context'];
  } else {
    $link_header = null;
  }
  if($link_header && $content_type !== 'application/ld+json') {
    // only 1 related link header permitted
    if(is_array($link_header)) {
      throw new JsonLdException(
        'URL could not be dereferenced, it has more than one ' .
        'associated HTTP Link Header.', 'jsonld.LoadDocumentError',
        'multiple context link headers', array('url' => $url));
    }
    $doc->{'contextUrl'} = $link_header->target;
  }

  // update document url based on redirects
  foreach($redirects as $redirect) {
    if(strpos($redirect, 'https') !== 0) {
      throw new JsonLdException(
        "Could not GET redirected url: '$redirect'; 'https' is required.",
        'jsonld.LoadDocumentError', 'loading document failed');
    }
    $url = $redirect;
  }
  $doc->document = $result;
  $doc->documentUrl = $url;
  return $doc;
}

/** Registered global RDF dataset parsers hashed by content-type. */
global $jsonld_rdf_parsers;
$jsonld_rdf_parsers = new stdClass();

/**
 * Registers a global RDF dataset parser by content-type, for use with
 * jsonld_from_rdf. Global parsers will be used by JsonLdProcessors that do
 * not register their own parsers.
 *
 * @param string $content_type the content-type for the parser.
 * @param callable $parser(input) the parser function (takes a string as
 *          a parameter and returns an RDF dataset).
 */
function jsonld_register_rdf_parser($content_type, $parser) {
  global $jsonld_rdf_parsers;
  $jsonld_rdf_parsers->{$content_type} = $parser;
}

/**
 * Unregisters a global RDF dataset parser by content-type.
 *
 * @param string $content_type the content-type for the parser.
 */
function jsonld_unregister_rdf_parser($content_type) {
  global $jsonld_rdf_parsers;
  if(property_exists($jsonld_rdf_parsers, $content_type)) {
    unset($jsonld_rdf_parsers->{$content_type});
  }
}

/**
 * Parses a URL into its component parts.
 *
 * @param string $url the URL to parse.
 *
 * @return assoc the parsed URL.
 */
function jsonld_parse_url($url) {
  if($url === null) {
    $url = '';
  }

  $keys = array(
    'href', 'protocol', 'scheme', '?authority', 'authority',
    '?auth', 'auth', 'user', 'pass', 'host', '?port', 'port', 'path',
    '?query', 'query', '?fragment', 'fragment');
  $regex = "/^(([^:\/?#]+):)?(\/\/(((([^:@]*)(?::([^:@]*))?)?@)?([^:\/?#]*)(:(\d*))?))?([^?#]*)(\?([^#]*))?(#(.*))?/";
  preg_match($regex, $url, $match);

  $rval = array();
  $flags = array();
  $len = count($keys);
  for($i = 0; $i < $len; ++$i) {
    $key = $keys[$i];
    if(strpos($key, '?') === 0) {
      $flags[substr($key, 1)] = !empty($match[$i]);
    } else if(!isset($match[$i])) {
      $rval[$key] = null;
    } else {
      $rval[$key] = $match[$i];
    }
  }

  if(!$flags['authority']) {
    $rval['authority'] = null;
  }
  if(!$flags['auth']) {
    $rval['auth'] = $rval['user'] = $rval['pass'] = null;
  }
  if(!$flags['port']) {
    $rval['port'] = null;
  }
  if(!$flags['query']) {
    $rval['query'] = null;
  }
  if(!$flags['fragment']) {
    $rval['fragment'] = null;
  }

  $rval['normalizedPath'] = jsonld_remove_dot_segments(
    $rval['path'], !!$rval['authority']);

  return $rval;
}

/**
 * Removes dot segments from a URL path.
 *
 * @param string $path the path to remove dot segments from.
 * @param bool $has_authority true if the URL has an authority, false if not.
 */
function jsonld_remove_dot_segments($path, $has_authority) {
  $rval = '';

  if(strpos($path, '/') === 0) {
    $rval = '/';
  }

  // RFC 3986 5.2.4 (reworked)
  $input = explode('/', $path);
  $output = array();
  while(count($input) > 0) {
    if($input[0] === '.' || ($input[0] === '' && count($input) > 1)) {
      array_shift($input);
      continue;
    }
    if($input[0] === '..') {
      array_shift($input);
      if($has_authority ||
        (count($output) > 0 && $output[count($output) - 1] !== '..')) {
        array_pop($output);
      } else {
        // leading relative URL '..'
        $output[] = '..';
      }
      continue;
    }
    $output[] = array_shift($input);
  }

  return $rval . implode('/', $output);
}

/**
 * Prepends a base IRI to the given relative IRI.
 *
 * @param mixed $base a string or the parsed base IRI.
 * @param string $iri the relative IRI.
 *
 * @return string the absolute IRI.
 */
function jsonld_prepend_base($base, $iri) {
  // skip IRI processing
  if($base === null) {
    return $iri;
  }

  // already an absolute IRI
  if(strpos($iri, ':') !== false) {
    return $iri;
  }

  // parse base if it is a string
  if(is_string($base)) {
    $base = jsonld_parse_url($base);
  }

  // parse given IRI
  $rel = jsonld_parse_url($iri);

  // per RFC3986 5.2.2
  $transform = array('protocol' => $base['protocol']);

  if($rel['authority'] !== null) {
    $transform['authority'] = $rel['authority'];
    $transform['path'] = $rel['path'];
    $transform['query'] = $rel['query'];
  } else {
    $transform['authority'] = $base['authority'];

    if($rel['path'] === '') {
      $transform['path'] = $base['path'];
      if($rel['query'] !== null) {
        $transform['query'] = $rel['query'];
      } else {
        $transform['query'] = $base['query'];
      }
    } else {
      if(strpos($rel['path'], '/') === 0) {
        // IRI represents an absolute path
        $transform['path'] = $rel['path'];
      } else {
        // merge paths
        $path = $base['path'];

        // append relative path to the end of the last directory from base
        if($rel['path'] !== '') {
          $idx = strrpos($path, '/');
          $idx = ($idx === false) ? 0 : $idx + 1;
          $path = substr($path, 0, $idx);
          if(strlen($path) > 0 && substr($path, -1) !== '/') {
            $path .= '/';
          }
          $path .= $rel['path'];
        }

        $transform['path'] = $path;
      }
      $transform['query'] = $rel['query'];
    }
  }

  // remove slashes and dots in path
  $transform['path'] = jsonld_remove_dot_segments(
    $transform['path'], !!$transform['authority']);

  // construct URL
  $rval = $transform['protocol'];
  if($transform['authority'] !== null) {
    $rval .= '//' . $transform['authority'];
  }
  $rval .= $transform['path'];
  if($transform['query'] !== null) {
    $rval .= '?' . $transform['query'];
  }
  if($rel['fragment'] !== null) {
    $rval .= '#' . $rel['fragment'];
  }

  // handle empty base
  if($rval === '') {
    $rval = './';
  }

  return $rval;
}

/**
 * Removes a base IRI from the given absolute IRI.
 *
 * @param mixed $base the base IRI.
 * @param string $iri the absolute IRI.
 *
 * @return string the relative IRI if relative to base, otherwise the absolute
 *           IRI.
 */
function jsonld_remove_base($base, $iri) {
  // skip IRI processing
  if($base === null) {
    return $iri;
  }

  if(is_string($base)) {
    $base = jsonld_parse_url($base);
  }

  // establish base root
  $root = '';
  if($base['href'] !== '') {
    $root .= "{$base['protocol']}//{$base['authority']}";
  } else if(strpos($iri, '//') === false) {
    // support network-path reference with empty base
    $root .= '//';
  }

  // IRI not relative to base
  if($root === '' || strpos($iri, $root) !== 0) {
    return $iri;
  }

  // remove root from IRI
  $rel = jsonld_parse_url(substr($iri, strlen($root)));

  // remove path segments that match (do not remove last segment unless there
  // is a hash or query)
  $base_segments = explode('/', $base['normalizedPath']);
  $iri_segments = explode('/', $rel['normalizedPath']);
  $last = ($rel['query'] || $rel['fragment']) ? 0 : 1;
  while(count($base_segments) > 0 && count($iri_segments) > $last) {
    if($base_segments[0] !== $iri_segments[0]) {
      break;
    }
    array_shift($base_segments);
    array_shift($iri_segments);
  }

  // use '../' for each non-matching base segment
  $rval = '';
  if(count($base_segments) > 0) {
    // don't count the last segment (if it ends with '/' last path doesn't
    // count and if it doesn't end with '/' it isn't a path)
    array_pop($base_segments);
    foreach($base_segments as $segment) {
      $rval .= '../';
    }
  }

  // prepend remaining segments
  $rval .= implode('/', $iri_segments);

  // add query and hash
  if($rel['query'] !== null) {
    $rval .= "?{$rel['query']}";
  }
  if($rel['fragment'] !== null) {
    $rval .= "#{$rel['fragment']}";
  }

  if($rval === '') {
    $rval = './';
  }

  return $rval;
}


/**
 * A JSON-LD processor.
 */
class JsonLdProcessor {
  /** XSD constants */
  const XSD_BOOLEAN = 'http://www.w3.org/2001/XMLSchema#boolean';
  const XSD_DOUBLE = 'http://www.w3.org/2001/XMLSchema#double';
  const XSD_INTEGER = 'http://www.w3.org/2001/XMLSchema#integer';
  const XSD_STRING = 'http://www.w3.org/2001/XMLSchema#string';

  /** RDF constants */
  const RDF_LIST = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#List';
  const RDF_FIRST = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#first';
  const RDF_REST = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#rest';
  const RDF_NIL = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#nil';
  const RDF_TYPE = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type';
  const RDF_LANGSTRING =
    'http://www.w3.org/1999/02/22-rdf-syntax-ns#langString';

  /** Restraints */
  const MAX_CONTEXT_URLS = 10;

  /** Processor-specific RDF dataset parsers. */
  protected $rdfParsers = null;

  /**
   * Constructs a JSON-LD processor.
   */
  public function __construct() {}

  /**
   * Performs JSON-LD compaction.
   *
   * @param mixed $input the JSON-LD object to compact.
   * @param mixed $ctx the context to compact with.
   * @param assoc $options the compaction options.
   *          [base] the base IRI to use.
   *          [compactArrays] true to compact arrays to single values when
   *            appropriate, false not to (default: true).
   *          [graph] true to always output a top-level graph (default: false).
   *          [skipExpansion] true to assume the input is expanded and skip
   *            expansion, false not to, defaults to false.
   *          [activeCtx] true to also return the active context used.
   *          [documentLoader(url)] the document loader.
   *
   * @return mixed the compacted JSON-LD output.
   */
  public function compact($input, $ctx, $options) {
    global $jsonld_default_load_document;

    if($ctx === null) {
      throw new JsonLdException(
        'The compaction context must not be null.',
        'jsonld.CompactError', 'invalid local context');
    }

    // nothing to compact
    if($input === null) {
      return null;
    }

    self::setdefaults($options, array(
      'base' => is_string($input) ? $input : '',
      'compactArrays' => true,
      'graph' => false,
      'skipExpansion' => false,
      'activeCtx' => false,
      'documentLoader' => $jsonld_default_load_document,
      'link' => false));
    if($options['link']) {
      // force skip expansion when linking, "link" is not part of the
      // public API, it should only be called from framing
      $options['skipExpansion'] = true;
    }

    if($options['skipExpansion'] === true) {
      $expanded = $input;
    } else {
      // expand input
      try {
        $expanded = $this->expand($input, $options);
      } catch(JsonLdException $e) {
        throw new JsonLdException(
          'Could not expand input before compaction.',
          'jsonld.CompactError', null, null, $e);
      }
    }

    // process context
    $active_ctx = $this->_getInitialContext($options);
    try {
      $active_ctx = $this->processContext($active_ctx, $ctx, $options);
    } catch(JsonLdException $e) {
      throw new JsonLdException(
        'Could not process context before compaction.',
        'jsonld.CompactError', null, null, $e);
    }

    // do compaction
    $compacted = $this->_compact($active_ctx, null, $expanded, $options);

    if($options['compactArrays'] &&
      !$options['graph'] && is_array($compacted)) {
      if(count($compacted) === 1) {
        // simplify to a single item
        $compacted = $compacted[0];
      } else if(count($compacted) === 0) {
        // simplify to an empty object
        $compacted = new stdClass();
      }
    } else if($options['graph']) {
      // always use array if graph option is on
      $compacted = self::arrayify($compacted);
    }

    // follow @context key
    if(is_object($ctx) && property_exists($ctx, '@context')) {
      $ctx = $ctx->{'@context'};
    }

    // build output context
    $ctx = self::copy($ctx);
    $ctx = self::arrayify($ctx);

    // remove empty contexts
    $tmp = $ctx;
    $ctx = array();
    foreach($tmp as $v) {
      if(!is_object($v) || count(array_keys((array)$v)) > 0) {
        $ctx[] = $v;
      }
    }

    // remove array if only one context
    $ctx_length = count($ctx);
    $has_context = ($ctx_length > 0);
    if($ctx_length === 1) {
      $ctx = $ctx[0];
    }

    // add context and/or @graph
    if(is_array($compacted)) {
      // use '@graph' keyword
      $kwgraph = $this->_compactIri($active_ctx, '@graph');
      $graph = $compacted;
      $compacted = new stdClass();
      if($has_context) {
        $compacted->{'@context'} = $ctx;
      }
      $compacted->{$kwgraph} = $graph;
    } else if(is_object($compacted) && $has_context) {
      // reorder keys so @context is first
      $graph = $compacted;
      $compacted = new stdClass();
      $compacted->{'@context'} = $ctx;
      foreach($graph as $k => $v) {
        $compacted->{$k} = $v;
      }
    }

    if($options['activeCtx']) {
      return array('compacted' => $compacted, 'activeCtx' => $active_ctx);
    }

    return $compacted;
  }

  /**
   * Performs JSON-LD expansion.
   *
   * @param mixed $input the JSON-LD object to expand.
   * @param assoc $options the options to use:
   *          [base] the base IRI to use.
   *          [expandContext] a context to expand with.
   *          [keepFreeFloatingNodes] true to keep free-floating nodes,
   *            false not to, defaults to false.
   *          [documentLoader(url)] the document loader.
   *
   * @return array the expanded JSON-LD output.
   */
  public function expand($input, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'keepFreeFloatingNodes' => false,
      'documentLoader' => $jsonld_default_load_document));

    // if input is a string, attempt to dereference remote document
    if(is_string($input)) {
      $remote_doc = call_user_func($options['documentLoader'], $input);
    } else {
      $remote_doc = (object)array(
        'contextUrl' => null,
        'documentUrl' => null,
        'document' => $input);
    }

    try {
      if($remote_doc->document === null) {
        throw new JsonLdException(
          'No remote document found at the given URL.',
          'jsonld.NullRemoteDocument');
      }
      if(is_string($remote_doc->document)) {
        $remote_doc->document = self::_parse_json($remote_doc->document);
      }
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not retrieve a JSON-LD document from the URL.',
        'jsonld.LoadDocumentError', 'loading document failed',
        array('remoteDoc' => $remote_doc), $e);
    }

    // set default base
    self::setdefault($options, 'base', $remote_doc->documentUrl ?: '');

    // build meta-object and retrieve all @context urls
    $input = (object)array(
      'document' => self::copy($remote_doc->document),
      'remoteContext' => (object)array(
        '@context' => $remote_doc->contextUrl));
    if(isset($options['expandContext'])) {
      $expand_context = self::copy($options['expandContext']);
      if(is_object($expand_context) &&
        property_exists($expand_context, '@context')) {
        $input->expandContext = $expand_context;
      } else {
        $input->expandContext = (object)array('@context' => $expand_context);
      }
    }

    // retrieve all @context URLs in the input
    try {
      $this->_retrieveContextUrls(
        $input, new stdClass(), $options['documentLoader'], $options['base']);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not perform JSON-LD expansion.',
        'jsonld.ExpandError', null, null, $e);
    }

    $active_ctx = $this->_getInitialContext($options);
    $document = $input->document;
    $remote_context = $input->remoteContext->{'@context'};

    // process optional expandContext
    if(property_exists($input, 'expandContext')) {
      $active_ctx = self::_processContext(
        $active_ctx, $input->expandContext, $options);
    }

    // process remote context from HTTP Link Header
    if($remote_context) {
      $active_ctx = self::_processContext(
        $active_ctx, $remote_context, $options);
    }

    // do expansion
    $expanded = $this->_expand($active_ctx, null, $document, $options, false);

    // optimize away @graph with no other properties
    if(is_object($expanded) && property_exists($expanded, '@graph') &&
      count(array_keys((array)$expanded)) === 1) {
      $expanded = $expanded->{'@graph'};
    } else if($expanded === null) {
      $expanded = array();
    }
    // normalize to an array
    return self::arrayify($expanded);
  }

  /**
   * Performs JSON-LD flattening.
   *
   * @param mixed $input the JSON-LD to flatten.
   * @param ctx the context to use to compact the flattened output, or null.
   * @param assoc $options the options to use:
   *          [base] the base IRI to use.
   *          [expandContext] a context to expand with.
   *          [documentLoader(url)] the document loader.
   *
   * @return array the flattened output.
   */
  public function flatten($input, $ctx, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'base' => is_string($input) ? $input : '',
      'documentLoader' => $jsonld_default_load_document));

    try {
      // expand input
      $expanded = $this->expand($input, $options);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not expand input before flattening.',
        'jsonld.FlattenError', null, null, $e);
    }

    // do flattening
    $flattened = $this->_flatten($expanded);

    if($ctx === null) {
      return $flattened;
    }

    // compact result (force @graph option to true, skip expansion)
    $options['graph'] = true;
    $options['skipExpansion'] = true;
    try {
      $compacted = $this->compact($flattened, $ctx, $options);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not compact flattened output.',
        'jsonld.FlattenError', null, null, $e);
    }

    return $compacted;
  }

  /**
   * Performs JSON-LD framing.
   *
   * @param mixed $input the JSON-LD object to frame.
   * @param stdClass $frame the JSON-LD frame to use.
   * @param $options the framing options.
   *          [base] the base IRI to use.
   *          [expandContext] a context to expand with.
   *          [embed] default @embed flag: '@last', '@always', '@never', '@link'
   *            (default: '@last').
   *          [explicit] default @explicit flag (default: false).
   *          [requireAll] default @requireAll flag (default: true).
   *          [omitDefault] default @omitDefault flag (default: false).
   *          [documentLoader(url)] the document loader.
   *
   * @return stdClass the framed JSON-LD output.
   */
  public function frame($input, $frame, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'base' => is_string($input) ? $input : '',
      'compactArrays' => true,
      'embed' => '@last',
      'explicit' => false,
      'requireAll' => true,
      'omitDefault' => false,
      'documentLoader' => $jsonld_default_load_document));

    // if frame is a string, attempt to dereference remote document
    if(is_string($frame)) {
      $remote_frame = call_user_func($options['documentLoader'], $frame);
    } else {
      $remote_frame = (object)array(
        'contextUrl' => null,
        'documentUrl' => null,
        'document' => $frame);
    }

    try {
      if($remote_frame->document === null) {
        throw new JsonLdException(
          'No remote document found at the given URL.',
          'jsonld.NullRemoteDocument');
      }
      if(is_string($remote_frame->document)) {
        $remote_frame->document = self::_parse_json($remote_frame->document);
      }
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not retrieve a JSON-LD document from the URL.',
        'jsonld.LoadDocumentError', 'loading document failed',
        array('remoteDoc' => $remote_frame), $e);
    }

    // preserve frame context
    $frame = $remote_frame->document;
    if($frame !== null) {
      $ctx = (property_exists($frame, '@context') ?
        $frame->{'@context'} : new stdClass());
      if($remote_frame->contextUrl !== null) {
        if($ctx !== null) {
          $ctx = $remote_frame->contextUrl;
        } else {
          $ctx = self::arrayify($ctx);
          $ctx[] = $remote_frame->contextUrl;
        }
        $frame->{'@context'} = $ctx;
      }
    }

    try {
      // expand input
      $expanded = $this->expand($input, $options);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not expand input before framing.',
        'jsonld.FrameError', null, null, $e);
    }

    try {
      // expand frame
      $opts = $options;
      $opts['keepFreeFloatingNodes'] = true;
      $expanded_frame = $this->expand($frame, $opts);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not expand frame before framing.',
        'jsonld.FrameError', null, null, $e);
    }

    // do framing
    $framed = $this->_frame($expanded, $expanded_frame, $options);

    try {
      // compact result (force @graph option to true, skip expansion, check
      // for linked embeds)
      $options['graph'] = true;
      $options['skipExpansion'] = true;
      $options['link'] = new ArrayObject();
      $options['activeCtx'] = true;
      $result = $this->compact($framed, $ctx, $options);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not compact framed output.',
        'jsonld.FrameError', null, null, $e);
    }

    $compacted = $result['compacted'];
    $active_ctx = $result['activeCtx'];

    // get graph alias
    $graph = $this->_compactIri($active_ctx, '@graph');
    // remove @preserve from results
    $options['link'] = new ArrayObject();
    $compacted->{$graph} = $this->_removePreserve(
      $active_ctx, $compacted->{$graph}, $options);
    return $compacted;
  }

  /**
   * Performs JSON-LD normalization.
   *
   * @param mixed $input the JSON-LD object to normalize.
   * @param assoc $options the options to use:
   *          [base] the base IRI to use.
   *          [expandContext] a context to expand with.
   *          [inputFormat] the format if input is not JSON-LD:
   *            'application/nquads' for N-Quads.
   *          [format] the format if output is a string:
   *            'application/nquads' for N-Quads.
   *          [documentLoader(url)] the document loader.
   *
   * @return mixed the normalized output.
   */
  public function normalize($input, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'base' => is_string($input) ? $input : '',
      'documentLoader' => $jsonld_default_load_document));

    if(isset($options['inputFormat'])) {
      if($options['inputFormat'] != 'application/nquads') {
         throw new JsonLdException(
           'Unknown normalization input format.', 'jsonld.NormalizeError');
      }
      $dataset = $this->parseNQuads($input);
    } else {
      try {
        // convert to RDF dataset then do normalization
        $opts = $options;
        if(isset($opts['format'])) {
          unset($opts['format']);
        }
        $opts['produceGeneralizedRdf'] = false;
        $dataset = $this->toRDF($input, $opts);
      } catch(Exception $e) {
        throw new JsonLdException(
          'Could not convert input to RDF dataset before normalization.',
          'jsonld.NormalizeError', null, null, $e);
      }
    }

    // do normalization
    return $this->_normalize($dataset, $options);
  }

  /**
   * Converts an RDF dataset to JSON-LD.
   *
   * @param mixed $dataset a serialized string of RDF in a format specified
   *          by the format option or an RDF dataset to convert.
   * @param assoc $options the options to use:
   *          [format] the format if input is a string:
   *            'application/nquads' for N-Quads (default).
   *          [useRdfType] true to use rdf:type, false to use @type
   *            (default: false).
   *          [useNativeTypes] true to convert XSD types into native types
   *            (boolean, integer, double), false not to (default: false).
   *
   * @return array the JSON-LD output.
   */
  public function fromRDF($dataset, $options) {
    global $jsonld_rdf_parsers;

    self::setdefaults($options, array(
      'useRdfType' => false,
      'useNativeTypes' => false));

    if(!isset($options['format']) && is_string($dataset)) {
      // set default format to nquads
      $options['format'] = 'application/nquads';
    }

    // handle special format
    if(isset($options['format']) && $options['format']) {
      // supported formats (processor-specific and global)
      if(($this->rdfParsers !== null &&
        !property_exists($this->rdfParsers, $options['format'])) ||
        $this->rdfParsers === null &&
        !property_exists($jsonld_rdf_parsers, $options['format'])) {
        throw new JsonLdException(
          'Unknown input format.',
          'jsonld.UnknownFormat', null, array('format' => $options['format']));
      }
      if($this->rdfParsers !== null) {
        $callable = $this->rdfParsers->{$options['format']};
      } else {
        $callable = $jsonld_rdf_parsers->{$options['format']};
      }
      $dataset = call_user_func($callable, $dataset);
    }

    // convert from RDF
    return $this->_fromRDF($dataset, $options);
  }

  /**
   * Outputs the RDF dataset found in the given JSON-LD object.
   *
   * @param mixed $input the JSON-LD object.
   * @param assoc $options the options to use:
   *          [base] the base IRI to use.
   *          [expandContext] a context to expand with.
   *          [format] the format to use to output a string:
   *            'application/nquads' for N-Quads.
   *          [produceGeneralizedRdf] true to output generalized RDF, false
   *            to produce only standard RDF (default: false).
   *          [documentLoader(url)] the document loader.
   *
   * @return mixed the resulting RDF dataset (or a serialization of it).
   */
  public function toRDF($input, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'base' => is_string($input) ? $input : '',
      'produceGeneralizedRdf' => false,
      'documentLoader' => $jsonld_default_load_document));

    try {
      // expand input
      $expanded = $this->expand($input, $options);
    } catch(JsonLdException $e) {
      throw new JsonLdException(
        'Could not expand input before serialization to RDF.',
        'jsonld.RdfError', null, null, $e);
    }

    // create node map for default graph (and any named graphs)
    $namer = new UniqueNamer('_:b');
    $node_map = (object)array('@default' => new stdClass());
    $this->_createNodeMap($expanded, $node_map, '@default', $namer);

    // output RDF dataset
    $dataset = new stdClass();
    $graph_names = array_keys((array)$node_map);
    sort($graph_names);
    foreach($graph_names as $graph_name) {
      $graph = $node_map->{$graph_name};
      // skip relative IRIs
      if($graph_name === '@default' || self::_isAbsoluteIri($graph_name)) {
        $dataset->{$graph_name} = $this->_graphToRDF($graph, $namer, $options);
      }
    }

    $rval = $dataset;

    // convert to output format
    if(isset($options['format']) && $options['format']) {
      // supported formats
      if($options['format'] === 'application/nquads') {
        $rval = self::toNQuads($dataset);
      } else {
        throw new JsonLdException(
          'Unknown output format.', 'jsonld.UnknownFormat',
          null, array('format' => $options['format']));
      }
    }

    return $rval;
  }

  /**
   * Processes a local context, resolving any URLs as necessary, and returns a
   * new active context in its callback.
   *
   * @param stdClass $active_ctx the current active context.
   * @param mixed $local_ctx the local context to process.
   * @param assoc $options the options to use:
   *          [documentLoader(url)] the document loader.
   *
   * @return stdClass the new active context.
   */
  public function processContext($active_ctx, $local_ctx, $options) {
    global $jsonld_default_load_document;
    self::setdefaults($options, array(
      'base' => '',
      'documentLoader' => $jsonld_default_load_document));

    // return initial context early for null context
    if($local_ctx === null) {
      return $this->_getInitialContext($options);
    }

    // retrieve URLs in local_ctx
    $local_ctx = self::copy($local_ctx);
    if(is_string($local_ctx) or (
      is_object($local_ctx) && !property_exists($local_ctx, '@context'))) {
      $local_ctx = (object)array('@context' => $local_ctx);
    }
    try {
      $this->_retrieveContextUrls(
        $local_ctx, new stdClass(),
        $options['documentLoader'], $options['base']);
    } catch(Exception $e) {
      throw new JsonLdException(
        'Could not process JSON-LD context.',
        'jsonld.ContextError', null, null, $e);
    }

    // process context
    return $this->_processContext($active_ctx, $local_ctx, $options);
  }

  /**
   * Returns true if the given subject has the given property.
   *
   * @param stdClass $subject the subject to check.
   * @param string $property the property to look for.
   *
   * @return bool true if the subject has the given property, false if not.
   */
  public static function hasProperty($subject, $property) {
    $rval = false;
    if(property_exists($subject, $property)) {
      $value = $subject->{$property};
      $rval = (!is_array($value) || count($value) > 0);
    }
    return $rval;
  }

  /**
   * Determines if the given value is a property of the given subject.
   *
   * @param stdClass $subject the subject to check.
   * @param string $property the property to check.
   * @param mixed $value the value to check.
   *
   * @return bool true if the value exists, false if not.
   */
  public static function hasValue($subject, $property, $value) {
    $rval = false;
    if(self::hasProperty($subject, $property)) {
      $val = $subject->{$property};
      $is_list = self::_isList($val);
      if(is_array($val) || $is_list) {
        if($is_list) {
          $val = $val->{'@list'};
        }
        foreach($val as $v) {
          if(self::compareValues($value, $v)) {
            $rval = true;
            break;
          }
        }
      } else if(!is_array($value)) {
        // avoid matching the set of values with an array value parameter
        $rval = self::compareValues($value, $val);
      }
    }
    return $rval;
  }

  /**
   * Adds a value to a subject. If the value is an array, all values in the
   * array will be added.
   *
   * Note: If the value is a subject that already exists as a property of the
   * given subject, this method makes no attempt to deeply merge properties.
   * Instead, the value will not be added.
   *
   * @param stdClass $subject the subject to add the value to.
   * @param string $property the property that relates the value to the subject.
   * @param mixed $value the value to add.
   * @param assoc [$options] the options to use:
   *          [propertyIsArray] true if the property is always an array, false
   *            if not (default: false).
   *          [allowDuplicate] true to allow duplicates, false not to (uses a
   *            simple shallow comparison of subject ID or value)
   *            (default: true).
   */
  public static function addValue(
    $subject, $property, $value, $options=array()) {
    self::setdefaults($options, array(
      'allowDuplicate' => true,
      'propertyIsArray' => false));

    if(is_array($value)) {
      if(count($value) === 0 && $options['propertyIsArray'] &&
        !property_exists($subject, $property)) {
        $subject->{$property} = array();
      }
      foreach($value as $v) {
        self::addValue($subject, $property, $v, $options);
      }
    } else if(property_exists($subject, $property)) {
      // check if subject already has value if duplicates not allowed
      $has_value = (!$options['allowDuplicate'] &&
        self::hasValue($subject, $property, $value));

      // make property an array if value not present or always an array
      if(!is_array($subject->{$property}) &&
        (!$has_value || $options['propertyIsArray'])) {
        $subject->{$property} = array($subject->{$property});
      }

      // add new value
      if(!$has_value) {
        $subject->{$property}[] = $value;
      }
    } else {
      // add new value as set or single value
      $subject->{$property} = ($options['propertyIsArray'] ?
        array($value) : $value);
    }
  }

  /**
   * Gets all of the values for a subject's property as an array.
   *
   * @param stdClass $subject the subject.
   * @param string $property the property.
   *
   * @return array all of the values for a subject's property as an array.
   */
  public static function getValues($subject, $property) {
    $rval = (property_exists($subject, $property) ?
      $subject->{$property} : array());
    return self::arrayify($rval);
  }

  /**
   * Removes a property from a subject.
   *
   * @param stdClass $subject the subject.
   * @param string $property the property.
   */
  public static function removeProperty($subject, $property) {
    unset($subject->{$property});
  }

  /**
   * Removes a value from a subject.
   *
   * @param stdClass $subject the subject.
   * @param string $property the property that relates the value to the subject.
   * @param mixed $value the value to remove.
   * @param assoc [$options] the options to use:
   *          [propertyIsArray] true if the property is always an array,
   *          false if not (default: false).
   */
  public static function removeValue(
    $subject, $property, $value, $options=array()) {
    self::setdefaults($options, array(
      'propertyIsArray' => false));

    // filter out value
    $filter = function($e) use ($value) {
      return !self::compareValues($e, $value);
    };
    $values = self::getValues($subject, $property);
    $values = array_values(array_filter($values, $filter));

    if(count($values) === 0) {
      self::removeProperty($subject, $property);
    } else if(count($values) === 1 && !$options['propertyIsArray']) {
      $subject->{$property} = $values[0];
    } else {
      $subject->{$property} = $values;
    }
  }

  /**
   * Compares two JSON-LD values for equality. Two JSON-LD values will be
   * considered equal if:
   *
   * 1. They are both primitives of the same type and value.
   * 2. They are both @values with the same @value, @type, @language,
   *   and @index, OR
   * 3. They both have @ids that are the same.
   *
   * @param mixed $v1 the first value.
   * @param mixed $v2 the second value.
   *
   * @return bool true if v1 and v2 are considered equal, false if not.
   */
  public static function compareValues($v1, $v2) {
    // 1. equal primitives
    if($v1 === $v2) {
      return true;
    }

    // 2. equal @values
    if(self::_isValue($v1) && self::_isValue($v2)) {
      return (
        self::_compareKeyValues($v1, $v2, '@value') &&
        self::_compareKeyValues($v1, $v2, '@type') &&
        self::_compareKeyValues($v1, $v2, '@language') &&
        self::_compareKeyValues($v1, $v2, '@index'));
    }

    // 3. equal @ids
    if(is_object($v1) && property_exists($v1, '@id') &&
      is_object($v2) && property_exists($v2, '@id')) {
      return $v1->{'@id'} === $v2->{'@id'};
    }

    return false;
  }

  /**
   * Gets the value for the given active context key and type, null if none is
   * set.
   *
   * @param stdClass $ctx the active context.
   * @param string $key the context key.
   * @param string [$type] the type of value to get (eg: '@id', '@type'), if not
   *          specified gets the entire entry for a key, null if not found.
   *
   * @return mixed the value.
   */
  public static function getContextValue($ctx, $key, $type) {
    $rval = null;

    // return null for invalid key
    if($key === null) {
      return $rval;
    }

    // get default language
    if($type === '@language' && property_exists($ctx, $type)) {
      $rval = $ctx->{$type};
    }

    // get specific entry information
    if(property_exists($ctx->mappings, $key)) {
      $entry = $ctx->mappings->{$key};
      if($entry === null) {
        return null;
      }

      if($type === null) {
        // return whole entry
        $rval = $entry;
      } else if(property_exists($entry, $type)) {
        // return entry value for type
        $rval = $entry->{$type};
      }
    }

    return $rval;
  }

  /**
   * Parses RDF in the form of N-Quads.
   *
   * @param string $input the N-Quads input to parse.
   *
   * @return stdClass an RDF dataset.
   */
  public static function parseNQuads($input) {
    // define partial regexes
    $iri = '(?:<([^:]+:[^>]*)>)';
    $bnode = '(_:(?:[A-Za-z][A-Za-z0-9]*))';
    $plain = '"([^"\\\\]*(?:\\\\.[^"\\\\]*)*)"';
    $datatype = "(?:\\^\\^$iri)";
    $language = '(?:@([a-z]+(?:-[a-z0-9]+)*))';
    $literal = "(?:$plain(?:$datatype|$language)?)";
    $ws = '[ \\t]';
    $eoln = '/(?:\r\n)|(?:\n)|(?:\r)/';
    $empty = "/^$ws*$/";

    // define quad part regexes
    $subject = "(?:$iri|$bnode)$ws+";
    $property = "$iri$ws+";
    $object = "(?:$iri|$bnode|$literal)$ws*";
    $graph_name = "(?:\\.|(?:(?:$iri|$bnode)$ws*\\.))";

    // full quad regex
    $quad = "/^$ws*$subject$property$object$graph_name$ws*$/";

    // build RDF dataset
    $dataset = new stdClass();

    // split N-Quad input into lines
    $lines = preg_split($eoln, $input);
    $line_number = 0;
    foreach($lines as $line) {
      $line_number += 1;

      // skip empty lines
      if(preg_match($empty, $line)) {
        continue;
      }

      // parse quad
      if(!preg_match($quad, $line, $match)) {
        throw new JsonLdException(
          'Error while parsing N-Quads; invalid quad.',
          'jsonld.ParseError', null, array('line' => $line_number));
      }

      // create RDF triple
      $triple = (object)array(
        'subject' => new stdClass(),
        'predicate' => new stdClass(),
        'object' => new stdClass());

      // get subject
      if($match[1] !== '') {
        $triple->subject->type = 'IRI';
        $triple->subject->value = $match[1];
      } else {
        $triple->subject->type = 'blank node';
        $triple->subject->value = $match[2];
      }

      // get predicate
      $triple->predicate->type = 'IRI';
      $triple->predicate->value = $match[3];

      // get object
      if($match[4] !== '') {
        $triple->object->type = 'IRI';
        $triple->object->value = $match[4];
      } else if($match[5] !== '') {
        $triple->object->type = 'blank node';
        $triple->object->value = $match[5];
      } else {
        $triple->object->type = 'literal';
        $unescaped = str_replace(
          array('\"', '\t', '\n', '\r', '\\\\'),
          array('"', "\t", "\n", "\r", '\\'),
          $match[6]);
        if(isset($match[7]) && $match[7] !== '') {
          $triple->object->datatype = $match[7];
        } else if(isset($match[8]) && $match[8] !== '') {
          $triple->object->datatype = self::RDF_LANGSTRING;
          $triple->object->language = $match[8];
        } else {
          $triple->object->datatype = self::XSD_STRING;
        }
        $triple->object->value = $unescaped;
      }

      // get graph name ('@default' is used for the default graph)
      $name = '@default';
      if(isset($match[9]) && $match[9] !== '') {
        $name = $match[9];
      } else if(isset($match[10]) && $match[10] !== '') {
        $name = $match[10];
      }

      // initialize graph in dataset
      if(!property_exists($dataset, $name)) {
        $dataset->{$name} = array($triple);
      } else {
        // add triple if unique to its graph
        $unique = true;
        $triples = &$dataset->{$name};
        foreach($triples as $t) {
          if(self::_compareRDFTriples($t, $triple)) {
            $unique = false;
            break;
          }
        }
        if($unique) {
          $triples[] = $triple;
        }
      }
    }

    return $dataset;
  }

  /**
   * Converts an RDF dataset to N-Quads.
   *
   * @param stdClass $dataset the RDF dataset to convert.
   *
   * @return string the N-Quads string.
   */
  public static function toNQuads($dataset) {
    $quads = array();
    foreach($dataset as $graph_name => $triples) {
      foreach($triples as $triple) {
        if($graph_name === '@default') {
          $graph_name = null;
        }
        $quads[] = self::toNQuad($triple, $graph_name);
      }
    }
    sort($quads);
    return implode($quads);
  }

  /**
   * Converts an RDF triple and graph name to an N-Quad string (a single quad).
   *
   * @param stdClass $triple the RDF triple to convert.
   * @param mixed $graph_name the name of the graph containing the triple, null
   *          for the default graph.
   * @param string $bnode the bnode the quad is mapped to (optional, for
   *          use during normalization only).
   *
   * @return string the N-Quad string.
   */
  public static function toNQuad($triple, $graph_name, $bnode=null) {
    $s = $triple->subject;
    $p = $triple->predicate;
    $o = $triple->object;
    $g = $graph_name;

    $quad = '';

    // subject is an IRI
    if($s->type === 'IRI') {
      $quad .= "<{$s->value}>";
    } else if($bnode !== null) {
      // bnode normalization mode
      $quad .= ($s->value === $bnode) ? '_:a' : '_:z';
    } else {
      // bnode normal mode
      $quad .= $s->value;
    }
    $quad .= ' ';

    // predicate is an IRI
    if($p->type === 'IRI') {
      $quad .= "<{$p->value}>";
    } else if($bnode !== null) {
      // FIXME: TBD what to do with bnode predicates during normalization
      // bnode normalization mode
      $quad .= '_:p';
    } else {
      // bnode normal mode
      $quad .= $p->value;
    }
    $quad .= ' ';

    // object is IRI, bnode, or literal
    if($o->type === 'IRI') {
      $quad .= "<{$o->value}>";
    } else if($o->type === 'blank node') {
      if($bnode !== null) {
        // normalization mode
        $quad .= ($o->value === $bnode) ? '_:a' : '_:z';
      } else {
        // normal mode
        $quad .= $o->value;
      }
    } else {
      $escaped = str_replace(
        array('\\', "\t", "\n", "\r", '"'),
        array('\\\\', '\t', '\n', '\r', '\"'),
        $o->value);
      $quad .= '"' . $escaped . '"';
      if($o->datatype === self::RDF_LANGSTRING) {
        if($o->language) {
          $quad .= "@{$o->language}";
        }
      } else if($o->datatype !== self::XSD_STRING) {
        $quad .= "^^<{$o->datatype}>";
      }
    }

    // graph
    if($g !== null) {
      if(strpos($g, '_:') !== 0) {
        $quad .= " <$g>";
      } else if($bnode) {
        $quad .= ' _:g';
      } else {
        $quad .= " $g";
      }
    }

    $quad .= " .\n";
    return $quad;
  }

  /**
   * Registers a processor-specific RDF dataset parser by content-type.
   * Global parsers will no longer be used by this processor.
   *
   * @param string $content_type the content-type for the parser.
   * @param callable $parser(input) the parser function (takes a string as
   *           a parameter and returns an RDF dataset).
   */
  public function registerRDFParser($content_type, $parser) {
    if($this->rdfParsers === null) {
      $this->rdfParsers = new stdClass();
    }
    $this->rdfParsers->{$content_type} = $parser;
  }

  /**
   * Unregisters a process-specific RDF dataset parser by content-type. If
   * there are no remaining processor-specific parsers, then the global
   * parsers will be re-enabled.
   *
   * @param string $content_type the content-type for the parser.
   */
  public function unregisterRDFParser($content_type) {
    if($this->rdfParsers !== null &&
      property_exists($this->rdfParsers, $content_type)) {
      unset($this->rdfParsers->{$content_type});
      if(count(get_object_vars($content_type)) === 0) {
        $this->rdfParsers = null;
      }
    }
  }

  /**
   * If $value is an array, returns $value, otherwise returns an array
   * containing $value as the only element.
   *
   * @param mixed $value the value.
   *
   * @return array an array.
   */
  public static function arrayify($value) {
    return is_array($value) ? $value : array($value);
  }

  /**
   * Clones an object, array, or string/number.
   *
   * @param mixed $value the value to clone.
   *
   * @return mixed the cloned value.
   */
  public static function copy($value) {
    if(is_object($value) || is_array($value)) {
      return unserialize(serialize($value));
    }
    return $value;
  }

  /**
   * Sets the value of a key for the given array if that property
   * has not already been set.
   *
   * @param &assoc $arr the object to update.
   * @param string $key the key to update.
   * @param mixed $value the value to set.
   */
  public static function setdefault(&$arr, $key, $value) {
    isset($arr[$key]) or $arr[$key] = $value;
  }

  /**
   * Sets default values for keys in the given array.
   *
   * @param &assoc $arr the object to update.
   * @param assoc $defaults the default keys and values.
   */
  public static function setdefaults(&$arr, $defaults) {
    foreach($defaults as $key => $value) {
      self::setdefault($arr, $key, $value);
    }
  }

  /**
   * Recursively compacts an element using the given active context. All values
   * must be in expanded form before this method is called.
   *
   * @param stdClass $active_ctx the active context to use.
   * @param mixed $active_property the compacted property with the element
   *          to compact, null for none.
   * @param mixed $element the element to compact.
   * @param assoc $options the compaction options.
   *
   * @return mixed the compacted value.
   */
  protected function _compact(
    $active_ctx, $active_property, $element, $options) {
    // recursively compact array
    if(is_array($element)) {
      $rval = array();
      foreach($element as $e) {
        // compact, dropping any null values
        $compacted = $this->_compact(
          $active_ctx, $active_property, $e, $options);
        if($compacted !== null) {
          $rval[] = $compacted;
        }
      }
      if($options['compactArrays'] && count($rval) === 1) {
        // use single element if no container is specified
        $container = self::getContextValue(
          $active_ctx, $active_property, '@container');
        if($container === null) {
          $rval = $rval[0];
        }
      }
      return $rval;
    }

    // recursively compact object
    if(is_object($element)) {
      if($options['link'] && property_exists($element, '@id') &&
        isset($options['link'][$element->{'@id'}])) {
        // check for a linked element to reuse
        $linked = $options['link'][$element->{'@id'}];
        foreach($linked as $link) {
          if($link['expanded'] === $element) {
            return $link['compacted'];
          }
        }
      }

      // do value compaction on @values and subject references
      if(self::_isValue($element) || self::_isSubjectReference($element)) {
        $rval = $this->_compactValue($active_ctx, $active_property, $element);
        if($options['link'] && self::_isSubjectReference($element)) {
          // store linked element
          if(!isset($options['link'][$element->{'@id'}])) {
            $options['link'][$element->{'@id'}] = array();
          }
          $options['link'][$element->{'@id'}][] = array(
            'expanded' => $element, 'compacted' => $rval);
        }
        return $rval;
      }

      // FIXME: avoid misuse of active property as an expanded property?
      $inside_reverse = ($active_property === '@reverse');

      $rval = new stdClass();

      if($options['link'] && property_exists($element, '@id')) {
        // store linked element
        if(!isset($options['link'][$element->{'@id'}])) {
          $options['link'][$element->{'@id'}] = array();
        }
        $options['link'][$element->{'@id'}][] = array(
          'expanded' => $element, 'compacted' => $rval);
      }

      // process element keys in order
      $keys = array_keys((array)$element);
      sort($keys);
      foreach($keys as $expanded_property) {
        $expanded_value = $element->{$expanded_property};

        // compact @id and @type(s)
        if($expanded_property === '@id' || $expanded_property === '@type') {
          if(is_string($expanded_value)) {
            // compact single @id
            $compacted_value = $this->_compactIri(
              $active_ctx, $expanded_value, null,
              array('vocab' => ($expanded_property === '@type')));
          } else {
            // expanded value must be a @type array
            $compacted_value = array();
            foreach($expanded_value as $ev) {
              $compacted_value[] = $this->_compactIri(
                $active_ctx, $ev, null, array('vocab' => true));
            }
          }

          // use keyword alias and add value
          $alias = $this->_compactIri($active_ctx, $expanded_property);
          $is_array = (is_array($compacted_value) &&
            count($expanded_value) === 0);
          self::addValue(
            $rval, $alias, $compacted_value,
            array('propertyIsArray' => $is_array));
          continue;
        }

        // handle @reverse
        if($expanded_property === '@reverse') {
          // recursively compact expanded value
          $compacted_value = $this->_compact(
            $active_ctx, '@reverse', $expanded_value, $options);

          // handle double-reversed properties
          foreach($compacted_value as $compacted_property => $value) {
            if(property_exists($active_ctx->mappings, $compacted_property) &&
              $active_ctx->mappings->{$compacted_property} &&
              $active_ctx->mappings->{$compacted_property}->reverse) {
                $container = self::getContextValue(
                  $active_ctx, $compacted_property, '@container');
              $use_array = ($container === '@set' ||
                !$options['compactArrays']);
              self::addValue(
                $rval, $compacted_property, $value,
                array('propertyIsArray' => $use_array));
              unset($compacted_value->{$compacted_property});
            }
          }

          if(count(array_keys((array)$compacted_value)) > 0) {
            // use keyword alias and add value
            $alias = $this->_compactIri($active_ctx, $expanded_property);
            self::addValue($rval, $alias, $compacted_value);
          }

          continue;
        }

        // handle @index property
        if($expanded_property === '@index') {
          // drop @index if inside an @index container
          $container = self::getContextValue(
            $active_ctx, $active_property, '@container');
          if($container === '@index') {
            continue;
          }

          // use keyword alias and add value
          $alias = $this->_compactIri($active_ctx, $expanded_property);
          self::addValue($rval, $alias, $expanded_value);
          continue;
        }

        // skip array processing for keywords that aren't @graph or @list
        if($expanded_property !== '@graph' && $expanded_property !== '@list' &&
          self::_isKeyword($expanded_property)) {
          // use keyword alias and add value as is
          $alias = $this->_compactIri($active_ctx, $expanded_property);
          self::addValue($rval, $alias, $expanded_value);
          continue;
        }

        // Note: expanded value must be an array due to expansion algorithm.

        // preserve empty arrays
        if(count($expanded_value) === 0) {
          $item_active_property = $this->_compactIri(
            $active_ctx, $expanded_property, $expanded_value,
            array('vocab' => true), $inside_reverse);
          self::addValue(
            $rval, $item_active_property, array(),
            array('propertyIsArray' => true));
        }

        // recusively process array values
        foreach($expanded_value as $expanded_item) {
          // compact property and get container type
          $item_active_property = $this->_compactIri(
            $active_ctx, $expanded_property, $expanded_item,
            array('vocab' => true), $inside_reverse);
          $container = self::getContextValue(
            $active_ctx, $item_active_property, '@container');

          // get @list value if appropriate
          $is_list = self::_isList($expanded_item);
          $list = null;
          if($is_list) {
            $list = $expanded_item->{'@list'};
          }

          // recursively compact expanded item
          $compacted_item = $this->_compact(
            $active_ctx, $item_active_property,
            $is_list ? $list : $expanded_item, $options);

          // handle @list
          if($is_list) {
            // ensure @list value is an array
            $compacted_item = self::arrayify($compacted_item);

            if($container !== '@list') {
              // wrap using @list alias
              $compacted_item = (object)array(
                $this->_compactIri($active_ctx, '@list') => $compacted_item);

              // include @index from expanded @list, if any
              if(property_exists($expanded_item, '@index')) {
                $compacted_item->{$this->_compactIri($active_ctx, '@index')} =
                  $expanded_item->{'@index'};
              }
            } else if(property_exists($rval, $item_active_property)) {
              // can't use @list container for more than 1 list
              throw new JsonLdException(
                'JSON-LD compact error; property has a "@list" @container ' .
                'rule but there is more than a single @list that matches ' .
                'the compacted term in the document. Compaction might mix ' .
                'unwanted items into the list.', 'jsonld.SyntaxError',
                'compaction to list of lists');
            }
          }

          // handle language and index maps
          if($container === '@language' || $container === '@index') {
            // get or create the map object
            if(property_exists($rval, $item_active_property)) {
              $map_object = $rval->{$item_active_property};
            } else {
              $rval->{$item_active_property} = $map_object = new stdClass();
            }

            // if container is a language map, simplify compacted value to
            // a simple string
            if($container === '@language' && self::_isValue($compacted_item)) {
              $compacted_item = $compacted_item->{'@value'};
            }

            // add compact value to map object using key from expanded value
            // based on the container type
            self::addValue(
              $map_object, $expanded_item->{$container}, $compacted_item);
          } else {
            // use an array if: compactArrays flag is false,
            // @container is @set or @list, value is an empty
            // array, or key is @graph
            $is_array = (!$options['compactArrays'] ||
              $container === '@set' || $container === '@list' ||
              (is_array($compacted_item) && count($compacted_item) === 0) ||
              $expanded_property === '@list' ||
              $expanded_property === '@graph');

            // add compact value
            self::addValue(
              $rval, $item_active_property, $compacted_item,
              array('propertyIsArray' => $is_array));
          }
        }
      }

      return $rval;
    }

    // only primitives remain which are already compact
    return $element;
  }

  /**
   * Recursively expands an element using the given context. Any context in
   * the element will be removed. All context URLs must have been retrieved
   * before calling this method.
   *
   * @param stdClass $active_ctx the active context to use.
   * @param mixed $active_property the property for the element, null for none.
   * @param mixed $element the element to expand.
   * @param assoc $options the expansion options.
   * @param bool $inside_list true if the property is a list, false if not.
   *
   * @return mixed the expanded value.
   */
  protected function _expand(
    $active_ctx, $active_property, $element, $options, $inside_list) {
    // nothing to expand
    if($element === null) {
      return $element;
    }

    // recursively expand array
    if(is_array($element)) {
      $rval = array();
      $container = self::getContextValue(
        $active_ctx, $active_property, '@container');
      $inside_list = $inside_list || $container === '@list';
      foreach($element as $e) {
        // expand element
        $e = $this->_expand(
          $active_ctx, $active_property, $e, $options, $inside_list);
        if($inside_list && (is_array($e) || self::_isList($e))) {
          // lists of lists are illegal
          throw new JsonLdException(
            'Invalid JSON-LD syntax; lists of lists are not permitted.',
            'jsonld.SyntaxError', 'list of lists');
        }
        // drop null values
        if($e !== null) {
          if(is_array($e)) {
            $rval = array_merge($rval, $e);
          } else {
            $rval[] = $e;
          }
        }
      }
      return $rval;
    }

    if(!is_object($element)) {
      // drop free-floating scalars that are not in lists
      if(!$inside_list &&
        ($active_property === null ||
        $this->_expandIri($active_ctx, $active_property,
          array('vocab' => true)) === '@graph')) {
        return null;
      }

      // expand element according to value expansion rules
      return $this->_expandValue($active_ctx, $active_property, $element);
    }

    // recursively expand object:

    // if element has a context, process it
    if(property_exists($element, '@context')) {
      $active_ctx = $this->_processContext(
        $active_ctx, $element->{'@context'}, $options);
    }

    // expand the active property
    $expanded_active_property = $this->_expandIri(
      $active_ctx, $active_property, array('vocab' => true));

    $rval = new stdClass();
    $keys = array_keys((array)$element);
    sort($keys);
    foreach($keys as $key) {
      $value = $element->{$key};

      if($key === '@context') {
        continue;
      }

      // expand key to IRI
      $expanded_property = $this->_expandIri(
        $active_ctx, $key, array('vocab' => true));

      // drop non-absolute IRI keys that aren't keywords
      if($expanded_property === null ||
        !(self::_isAbsoluteIri($expanded_property) ||
        self::_isKeyword($expanded_property))) {
        continue;
      }

      if(self::_isKeyword($expanded_property)) {
        if($expanded_active_property === '@reverse') {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; a keyword cannot be used as a @reverse ' .
            'property.', 'jsonld.SyntaxError', 'invalid reverse property map',
            array('value' => $value));
        }
        if(property_exists($rval, $expanded_property)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; colliding keywords detected.',
            'jsonld.SyntaxError', 'colliding keywords',
            array('keyword' => $expanded_property));
        }
      }

      // syntax error if @id is not a string
      if($expanded_property === '@id' && !is_string($value)) {
        if(!isset($options['isFrame']) || !$options['isFrame']) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; "@id" value must a string.',
            'jsonld.SyntaxError', 'invalid @id value',
            array('value' => $value));
        }
        if(!is_object($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; "@id" value must a string or an object.',
            'jsonld.SyntaxError', 'invalid @id value',
            array('value' => $value));
        }
      }

      // validate @type value
      if($expanded_property === '@type') {
        $this->_validateTypeValue($value);
      }

      // @graph must be an array or an object
      if($expanded_property === '@graph' &&
        !(is_object($value) || is_array($value))) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; "@graph" value must not be an ' .
          'object or an array.', 'jsonld.SyntaxError',
          'invalid @graph value', array('value' => $value));
      }

      // @value must not be an object or an array
      if($expanded_property === '@value' &&
        (is_object($value) || is_array($value))) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; "@value" value must not be an ' .
          'object or an array.', 'jsonld.SyntaxError',
          'invalid value object value', array('value' => $value));
      }

      // @language must be a string
      if($expanded_property === '@language') {
        if($value === null) {
          // drop null @language values, they expand as if they didn't exist
          continue;
        }
        if(!is_string($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; "@language" value must not be a string.',
            'jsonld.SyntaxError', 'invalid language-tagged string',
            array('value' => $value));
        }
        // ensure language value is lowercase
        $value = strtolower($value);
      }

      // @index must be a string
      if($expanded_property === '@index') {
        if(!is_string($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; "@index" value must be a string.',
            'jsonld.SyntaxError', 'invalid @index value',
            array('value' => $value));
        }
      }

      // @reverse must be an object
      if($expanded_property === '@reverse') {
        if(!is_object($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; "@reverse" value must be an object.',
            'jsonld.SyntaxError', 'invalid @reverse value',
            array('value' => $value));
        }

        $expanded_value = $this->_expand(
          $active_ctx, '@reverse', $value, $options, $inside_list);

        // properties double-reversed
        if(property_exists($expanded_value, '@reverse')) {
          foreach($expanded_value->{'@reverse'} as $rproperty => $rvalue) {
            self::addValue(
              $rval, $rproperty, $rvalue, array('propertyIsArray' => true));
          }
        }

        // FIXME: can this be merged with code below to simplify?
        // merge in all reversed properties
        if(property_exists($rval, '@reverse')) {
          $reverse_map = $rval->{'@reverse'};
        } else {
          $reverse_map = null;
        }
        foreach($expanded_value as $property => $items) {
          if($property === '@reverse') {
            continue;
          }
          if($reverse_map === null) {
            $reverse_map = $rval->{'@reverse'} = new stdClass();
          }
          self::addValue(
            $reverse_map, $property, array(),
            array('propertyIsArray' => true));
          foreach($items as $item) {
            if(self::_isValue($item) || self::_isList($item)) {
              throw new JsonLdException(
                'Invalid JSON-LD syntax; "@reverse" value must not be a ' +
                '@value or an @list.', 'jsonld.SyntaxError',
                'invalid reverse property value',
                array('value' => $expanded_value));
            }
            self::addValue(
              $reverse_map, $property, $item,
              array('propertyIsArray' => true));
          }
        }

        continue;
      }

      $container = self::getContextValue($active_ctx, $key, '@container');

      if($container === '@language' && is_object($value)) {
        // handle language map container (skip if value is not an object)
        $expanded_value = $this->_expandLanguageMap($value);
      } else if($container === '@index' && is_object($value)) {
        // handle index container (skip if value is not an object)
        $expanded_value = array();
        $value_keys = array_keys((array)$value);
        sort($value_keys);
        foreach($value_keys as $value_key) {
          $val = $value->{$value_key};
          $val = self::arrayify($val);
          $val = $this->_expand($active_ctx, $key, $val, $options, false);
          foreach($val as $item) {
            if(!property_exists($item, '@index')) {
              $item->{'@index'} = $value_key;
            }
            $expanded_value[] = $item;
          }
        }
      } else {
        // recurse into @list or @set
        $is_list = ($expanded_property === '@list');
        if($is_list || $expanded_property === '@set') {
          $next_active_property = $active_property;
          if($is_list && $expanded_active_property === '@graph') {
            $next_active_property = null;
          }
          $expanded_value = $this->_expand(
            $active_ctx, $next_active_property, $value, $options, $is_list);
          if($is_list && self::_isList($expanded_value)) {
            throw new JsonLdException(
              'Invalid JSON-LD syntax; lists of lists are not permitted.',
              'jsonld.SyntaxError', 'list of lists');
          }
        } else {
          // recursively expand value with key as new active property
          $expanded_value = $this->_expand(
            $active_ctx, $key, $value, $options, false);
        }
      }

      // drop null values if property is not @value
      if($expanded_value === null && $expanded_property !== '@value') {
        continue;
      }

      // convert expanded value to @list if container specifies it
      if($expanded_property !== '@list' && !self::_isList($expanded_value) &&
        $container === '@list') {
        // ensure expanded value is an array
        $expanded_value = (object)array(
          '@list' => self::arrayify($expanded_value));
      }

      // FIXME: can this be merged with code above to simplify?
      // merge in reverse properties
      if(property_exists($active_ctx->mappings, $key) &&
        $active_ctx->mappings->{$key} &&
        $active_ctx->mappings->{$key}->reverse) {
        if(property_exists($rval, '@reverse')) {
          $reverse_map = $rval->{'@reverse'};
        } else {
          $reverse_map = $rval->{'@reverse'} = new stdClass();
        }
        $expanded_value = self::arrayify($expanded_value);
        foreach($expanded_value as $item) {
          if(self::_isValue($item) || self::_isList($item)) {
            throw new JsonLdException(
              'Invalid JSON-LD syntax; "@reverse" value must not be a ' +
              '@value or an @list.', 'jsonld.SyntaxError',
              'invalid reverse property value',
              array('value' => $expanded_value));
          }
          self::addValue(
            $reverse_map, $expanded_property, $item,
            array('propertyIsArray' => true));
        }
        continue;
      }

      // add value for property
      // use an array except for certain keywords
      $use_array = (!in_array(
        $expanded_property, array(
          '@index', '@id', '@type', '@value', '@language')));
      self::addValue(
        $rval, $expanded_property, $expanded_value,
        array('propertyIsArray' => $use_array));
    }

    // get property count on expanded output
    $keys = array_keys((array)$rval);
    $count = count($keys);

    // @value must only have @language or @type
    if(property_exists($rval, '@value')) {
      // @value must only have @language or @type
      if(property_exists($rval, '@type') &&
        property_exists($rval, '@language')) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; an element containing "@value" may not ' .
          'contain both "@type" and "@language".',
          'jsonld.SyntaxError', 'invalid value object',
          array('element' => $rval));
      }
      $valid_count = $count - 1;
      if(property_exists($rval, '@type')) {
        $valid_count -= 1;
      }
      if(property_exists($rval, '@index')) {
        $valid_count -= 1;
      }
      if(property_exists($rval, '@language')) {
        $valid_count -= 1;
      }
      if($valid_count !== 0) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; an element containing "@value" may only ' .
          'have an "@index" property and at most one other property ' .
          'which can be "@type" or "@language".',
          'jsonld.SyntaxError', 'invalid value object',
          array('element' => $rval));
      }
      // drop null @values
      if($rval->{'@value'} === null) {
        $rval = null;
      } else if(property_exists($rval, '@language') &&
        !is_string($rval->{'@value'})) {
        // if @language is present, @value must be a string
        throw new JsonLdException(
          'Invalid JSON-LD syntax; only strings may be language-tagged.',
          'jsonld.SyntaxError', 'invalid language-tagged value',
          array('element' => $rval));
      } else if(property_exists($rval, '@type') &&
        (!self::_isAbsoluteIri($rval->{'@type'}) ||
        strpos($rval->{'@type'}, '_:') === 0)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; an element containing "@value" ' .
          'and "@type" must have an absolute IRI for the value ' .
          'of "@type".', 'jsonld.SyntaxError', 'invalid typed value',
          array('element' => $rval));
      }
    } else if(property_exists($rval, '@type') && !is_array($rval->{'@type'})) {
      // convert @type to an array
      $rval->{'@type'} = array($rval->{'@type'});
    } else if(property_exists($rval, '@set') ||
      property_exists($rval, '@list')) {
      // handle @set and @list
      if($count > 1 && !($count === 2 && property_exists($rval, '@index'))) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; if an element has the property "@set" ' .
          'or "@list", then it can have at most one other property that is ' .
          '"@index".', 'jsonld.SyntaxError', 'invalid set or list object',
          array('element' => $rval));
      }
      // optimize away @set
      if(property_exists($rval, '@set')) {
        $rval = $rval->{'@set'};
        $keys = array_keys((array)$rval);
        $count = count($keys);
      }
    } else if($count === 1 && property_exists($rval, '@language')) {
      // drop objects with only @language
      $rval = null;
    }

    // drop certain top-level objects that do not occur in lists
    if(is_object($rval) &&
      !$options['keepFreeFloatingNodes'] && !$inside_list &&
      ($active_property === null || $expanded_active_property === '@graph')) {
      // drop empty object or top-level @value/@list, or object with only @id
      if($count === 0 || property_exists($rval, '@value') ||
        property_exists($rval, '@list') ||
        ($count === 1 && property_exists($rval, '@id'))) {
        $rval = null;
      }
    }

    return $rval;
  }

  /**
   * Performs JSON-LD flattening.
   *
   * @param array $input the expanded JSON-LD to flatten.
   *
   * @return array the flattened output.
   */
  protected function _flatten($input) {
    // produce a map of all subjects and name each bnode
    $namer = new UniqueNamer('_:b');
    $graphs = (object)array('@default' => new stdClass());
    $this->_createNodeMap($input, $graphs, '@default', $namer);

    // add all non-default graphs to default graph
    $default_graph = $graphs->{'@default'};
    $graph_names = array_keys((array)$graphs);
    foreach($graph_names as $graph_name) {
      if($graph_name === '@default') {
        continue;
      }
      $node_map = $graphs->{$graph_name};
      if(!property_exists($default_graph, $graph_name)) {
        $default_graph->{$graph_name} = (object)array(
          '@id' => $graph_name, '@graph' => array());
      }
      $subject = $default_graph->{$graph_name};
      if(!property_exists($subject, '@graph')) {
        $subject->{'@graph'} = array();
      }
      $ids = array_keys((array)$node_map);
      sort($ids);
      foreach($ids as $id) {
        $node = $node_map->{$id};
        // only add full subjects
        if(!self::_isSubjectReference($node)) {
          $subject->{'@graph'}[] = $node;
        }
      }
    }

    // produce flattened output
    $flattened = array();
    $keys = array_keys((array)$default_graph);
    sort($keys);
    foreach($keys as $key) {
      $node = $default_graph->{$key};
      // only add full subjects to top-level
      if(!self::_isSubjectReference($node)) {
        $flattened[] = $node;
      }
    }
    return $flattened;
  }

  /**
   * Performs JSON-LD framing.
   *
   * @param array $input the expanded JSON-LD to frame.
   * @param array $frame the expanded JSON-LD frame to use.
   * @param assoc $options the framing options.
   *
   * @return array the framed output.
   */
  protected function _frame($input, $frame, $options) {
    // create framing state
    $state = (object)array(
      'options' => $options,
      'graphs' => (object)array(
        '@default' => new stdClass(),
        '@merged' => new stdClass()),
      'subjectStack' => array(),
      'link' => new stdClass());

    // produce a map of all graphs and name each bnode
    // FIXME: currently uses subjects from @merged graph only
    $namer = new UniqueNamer('_:b');
    $this->_createNodeMap($input, $state->graphs, '@merged', $namer);
    $state->subjects = $state->graphs->{'@merged'};

    // frame the subjects
    $framed = new ArrayObject();
    $keys = array_keys((array)$state->subjects);
    sort($keys);
    $this->_matchFrame($state, $keys, $frame, $framed, null);
    return (array)$framed;
  }

  /**
   * Performs normalization on the given RDF dataset.
   *
   * @param stdClass $dataset the RDF dataset to normalize.
   * @param assoc $options the normalization options.
   *
   * @return mixed the normalized output.
   */
  protected function _normalize($dataset, $options) {
    // create quads and map bnodes to their associated quads
    $quads = array();
    $bnodes = new stdClass();
    foreach($dataset as $graph_name => $triples) {
      if($graph_name === '@default') {
        $graph_name = null;
      }
      foreach($triples as $triple) {
        $quad = $triple;
        if($graph_name !== null) {
          if(strpos($graph_name, '_:') === 0) {
            $quad->name = (object)array(
              'type' => 'blank node', 'value' => $graph_name);
          } else {
            $quad->name = (object)array(
              'type' => 'IRI', 'value' => $graph_name);
          }
        }
        $quads[] = $quad;

        foreach(array('subject', 'object', 'name') as $attr) {
          if(property_exists($quad, $attr) &&
            $quad->{$attr}->type === 'blank node') {
            $id = $quad->{$attr}->value;
            if(property_exists($bnodes, $id)) {
              $bnodes->{$id}->quads[] = $quad;
            } else {
              $bnodes->{$id} = (object)array('quads' => array($quad));
            }
          }
        }
      }
    }

    // mapping complete, start canonical naming
    $namer = new UniqueNamer('_:c14n');

    // continue to hash bnode quads while bnodes are assigned names
    $unnamed = null;
    $nextUnnamed = array_keys((array)$bnodes);
    $duplicates = null;
    do {
      $unnamed = $nextUnnamed;
      $nextUnnamed = array();
      $duplicates = new stdClass();
      $unique = new stdClass();
      foreach($unnamed as $bnode) {
        // hash quads for each unnamed bnode
        $hash = $this->_hashQuads($bnode, $bnodes, $namer);

        // store hash as unique or a duplicate
        if(property_exists($duplicates, $hash)) {
          $duplicates->{$hash}[] = $bnode;
          $nextUnnamed[] = $bnode;
        } else if(property_exists($unique, $hash)) {
          $duplicates->{$hash} = array($unique->{$hash}, $bnode);
          $nextUnnamed[] = $unique->{$hash};
          $nextUnnamed[] = $bnode;
          unset($unique->{$hash});
        } else {
          $unique->{$hash} = $bnode;
        }
      }

      // name unique bnodes in sorted hash order
      $hashes = array_keys((array)$unique);
      sort($hashes);
      foreach($hashes as $hash) {
        $namer->getName($unique->{$hash});
      }
    }
    while(count($unnamed) > count($nextUnnamed));

    // enumerate duplicate hash groups in sorted order
    $hashes = array_keys((array)$duplicates);
    sort($hashes);
    foreach($hashes as $hash) {
      // process group
      $group = $duplicates->{$hash};
      $results = array();
      foreach($group as $bnode) {
        // skip already-named bnodes
        if($namer->isNamed($bnode)) {
          continue;
        }

        // hash bnode paths
        $path_namer = new UniqueNamer('_:b');
        $path_namer->getName($bnode);
        $results[] = $this->_hashPaths($bnode, $bnodes, $namer, $path_namer);
      }

      // name bnodes in hash order
      usort($results, function($a, $b) {
        $a = $a->hash;
        $b = $b->hash;
        return ($a < $b) ? -1 : (($a > $b) ? 1 : 0);
      });
      foreach($results as $result) {
        // name all bnodes in path namer in key-entry order
        foreach($result->pathNamer->order as $bnode) {
          $namer->getName($bnode);
        }
      }
    }

    // create normalized array
    $normalized = array();

    /* Note: At this point all bnodes in the set of RDF quads have been
     assigned canonical names, which have been stored in the 'namer' object.
     Here each quad is updated by assigning each of its bnodes its new name
     via the 'namer' object. */

    // update bnode names in each quad and serialize
    foreach($quads as $quad) {
      foreach(array('subject', 'object', 'name') as $attr) {
        if(property_exists($quad, $attr) &&
          $quad->{$attr}->type === 'blank node' &&
          strpos($quad->{$attr}->value, '_:c14n') !== 0) {
          $quad->{$attr}->value = $namer->getName($quad->{$attr}->value);
        }
      }
      $normalized[] = $this->toNQuad($quad, property_exists($quad, 'name') ?
        $quad->name->value : null);
    }

    // sort normalized output
    sort($normalized);

    // handle output format
    if(isset($options['format']) && $options['format']) {
      if($options['format'] === 'application/nquads') {
        return implode($normalized);
      }
      throw new JsonLdException(
        'Unknown output format.',
        'jsonld.UnknownFormat', null, array('format' => $options['format']));
    }

    // return RDF dataset
    return $this->parseNQuads(implode($normalized));
  }

  /**
   * Converts an RDF dataset to JSON-LD.
   *
   * @param stdClass $dataset the RDF dataset.
   * @param assoc $options the RDF serialization options.
   *
   * @return array the JSON-LD output.
   */
  protected function _fromRDF($dataset, $options) {
    $default_graph = new stdClass();
    $graph_map = (object)array('@default' => $default_graph);
    $referenced_once = (object)array();

    foreach($dataset as $name => $graph) {
      if(!property_exists($graph_map, $name)) {
        $graph_map->{$name} = new stdClass();
      }
      if($name !== '@default' && !property_exists($default_graph, $name)) {
        $default_graph->{$name} = (object)array('@id' => $name);
      }
      $node_map = $graph_map->{$name};
      foreach($graph as $triple) {
        // get subject, predicate, object
        $s = $triple->subject->value;
        $p = $triple->predicate->value;
        $o = $triple->object;

        if(!property_exists($node_map, $s)) {
          $node_map->{$s} = (object)array('@id' => $s);
        }
        $node = $node_map->{$s};

        $object_is_id = ($o->type === 'IRI' || $o->type === 'blank node');
        if($object_is_id && !property_exists($node_map, $o->value)) {
          $node_map->{$o->value} = (object)array('@id' => $o->value);
        }

        if($p === self::RDF_TYPE && !$options['useRdfType'] && $object_is_id) {
          self::addValue(
            $node, '@type', $o->value, array('propertyIsArray' => true));
          continue;
        }

        $value = self::_RDFToObject($o, $options['useNativeTypes']);
        self::addValue($node, $p, $value, array('propertyIsArray' => true));

        // object may be an RDF list/partial list node but we can't know
        // easily until all triples are read
        if($object_is_id) {
          if($o->value === self::RDF_NIL) {
            $object = $node_map->{$o->value};
            if(!property_exists($object, 'usages')) {
              $object->usages = array();
            }
            $object->usages[] = (object)array(
              'node' => $node,
              'property' => $p,
              'value' => $value);
          } else if(property_exists($referenced_once, $o->value)) {
            // object referenced more than once
            $referenced_once->{$o->value} = false;
          } else {
            // track single reference
            $referenced_once->{$o->value} = (object)array(
              'node' => $node,
              'property' => $p,
              'value' => $value);
          }
        }
      }
    }

    // convert linked lists to @list arrays
    foreach($graph_map as $name => $graph_object) {
      // no @lists to be converted, continue
      if(!property_exists($graph_object, self::RDF_NIL)) {
        continue;
      }

      // iterate backwards through each RDF list
      $nil = $graph_object->{self::RDF_NIL};
      foreach($nil->usages as $usage) {
        $node = $usage->node;
        $property = $usage->property;
        $head = $usage->value;
        $list = array();
        $list_nodes = array();

        // ensure node is a well-formed list node; it must:
        // 1. Be referenced only once.
        // 2. Have an array for rdf:first that has 1 item.
        // 3. Have an array for rdf:rest that has 1 item.
        // 4. Have no keys other than: @id, rdf:first, rdf:rest, and,
        //   optionally, @type where the value is rdf:List.
        $node_key_count = count(array_keys((array)$node));
        while($property === self::RDF_REST &&
          property_exists($referenced_once, $node->{'@id'}) &&
          is_object($referenced_once->{$node->{'@id'}}) &&
          property_exists($node, self::RDF_FIRST) &&
          property_exists($node, self::RDF_REST) &&
          is_array($node->{self::RDF_FIRST}) &&
          is_array($node->{self::RDF_REST}) &&
          count($node->{self::RDF_FIRST}) === 1 &&
          count($node->{self::RDF_REST}) === 1 &&
          ($node_key_count === 3 || ($node_key_count === 4 &&
            property_exists($node, '@type') && is_array($node->{'@type'}) &&
            count($node->{'@type'}) === 1 &&
            $node->{'@type'}[0] === self::RDF_LIST))) {
          $list[] = $node->{self::RDF_FIRST}[0];
          $list_nodes[] = $node->{'@id'};

          // get next node, moving backwards through list
          $usage = $referenced_once->{$node->{'@id'}};
          $node = $usage->node;
          $property = $usage->property;
          $head = $usage->value;
          $node_key_count = count(array_keys((array)$node));

          // if node is not a blank node, then list head found
          if(strpos($node->{'@id'}, '_:') !== 0) {
            break;
          }
        }

        // list is nested in another list
        if($property === self::RDF_FIRST) {
          // empty list
          if($node->{'@id'} === self::RDF_NIL) {
            // can't convert rdf:nil to a @list object because it would
            // result in a list of lists which isn't supported
            continue;
          }

          // preserve list head
          $head = $graph_object->{$head->{'@id'}}->{self::RDF_REST}[0];
          array_pop($list);
          array_pop($list_nodes);
        }

        // transform list into @list object
        unset($head->{'@id'});
        $head->{'@list'} = array_reverse($list);
        foreach($list_nodes as $list_node) {
          unset($graph_object->{$list_node});
        }
      }

      unset($nil->usages);
    }

    $result = array();
    $subjects = array_keys((array)$default_graph);
    sort($subjects);
    foreach($subjects as $subject) {
      $node = $default_graph->{$subject};
      if(property_exists($graph_map, $subject)) {
        $node->{'@graph'} = array();
        $graph_object = $graph_map->{$subject};
        $subjects_ = array_keys((array)$graph_object);
        sort($subjects_);
        foreach($subjects_ as $subject_) {
          $node_ = $graph_object->{$subject_};
          // only add full subjects to top-level
          if(!self::_isSubjectReference($node_)) {
            $node->{'@graph'}[] = $node_;
          }
        }
      }
      // only add full subjects to top-level
      if(!self::_isSubjectReference($node)) {
        $result[] = $node;
      }
    }

    return $result;
  }

  /**
   * Processes a local context and returns a new active context.
   *
   * @param stdClass $active_ctx the current active context.
   * @param mixed $local_ctx the local context to process.
   * @param assoc $options the context processing options.
   *
   * @return stdClass the new active context.
   */
  protected function _processContext($active_ctx, $local_ctx, $options) {
    global $jsonld_cache;

    // normalize local context to an array
    if(is_object($local_ctx) && property_exists($local_ctx, '@context') &&
      is_array($local_ctx->{'@context'})) {
      $local_ctx = $local_ctx->{'@context'};
    }
    $ctxs = self::arrayify($local_ctx);

    // no contexts in array, clone existing context
    if(count($ctxs) === 0) {
      return self::_cloneActiveContext($active_ctx);
    }

    // process each context in order, update active context
    // on each iteration to ensure proper caching
    $rval = $active_ctx;
    foreach($ctxs as $ctx) {
      // reset to initial context
      if($ctx === null) {
        $rval = $active_ctx = $this->_getInitialContext($options);
        continue;
      }

      // dereference @context key if present
      if(is_object($ctx) && property_exists($ctx, '@context')) {
        $ctx = $ctx->{'@context'};
      }

      // context must be an object by now, all URLs retrieved before this call
      if(!is_object($ctx)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context must be an object.',
          'jsonld.SyntaxError', 'invalid local context',
          array('context' => $ctx));
      }

      // get context from cache if available
      if(property_exists($jsonld_cache, 'activeCtx')) {
        $cached = $jsonld_cache->activeCtx->get($active_ctx, $ctx);
        if($cached) {
          $rval = $active_ctx = $cached;
          $must_clone = true;
          continue;
        }
      }

      // update active context and clone new one before updating
      $active_ctx = $rval;
      $rval = self::_cloneActiveContext($rval);

      // define context mappings for keys in local context
      $defined = new stdClass();

      // handle @base
      if(property_exists($ctx, '@base')) {
        $base = $ctx->{'@base'};
        if($base === null) {
          $base = null;
        } else if(!is_string($base)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; the value of "@base" in a ' .
            '@context must be a string or null.',
            'jsonld.SyntaxError', 'invalid base IRI', array('context' => $ctx));
        } else if($base !== '' && !self::_isAbsoluteIri($base)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; the value of "@base" in a ' .
            '@context must be an absolute IRI or the empty string.',
            'jsonld.SyntaxError', 'invalid base IRI', array('context' => $ctx));
        }
        if($base !== null) {
          $base = jsonld_parse_url($base);
        }
        $rval->{'@base'} = $base;
        $defined->{'@base'} = true;
      }

      // handle @vocab
      if(property_exists($ctx, '@vocab')) {
        $value = $ctx->{'@vocab'};
        if($value === null) {
          unset($rval->{'@vocab'});
        } else if(!is_string($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; the value of "@vocab" in a ' .
            '@context must be a string or null.',
            'jsonld.SyntaxError', 'invalid vocab mapping',
            array('context' => $ctx));
        } else if(!self::_isAbsoluteIri($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; the value of "@vocab" in a ' .
            '@context must be an absolute IRI.',
            'jsonld.SyntaxError', 'invalid vocab mapping',
            array('context' => $ctx));
        } else {
          $rval->{'@vocab'} = $value;
        }
        $defined->{'@vocab'} = true;
      }

      // handle @language
      if(property_exists($ctx, '@language')) {
        $value = $ctx->{'@language'};
        if($value === null) {
          unset($rval->{'@language'});
        } else if(!is_string($value)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; the value of "@language" in a ' .
            '@context must be a string or null.',
            'jsonld.SyntaxError', 'invalid default language',
            array('context' => $ctx));
        } else {
          $rval->{'@language'} = strtolower($value);
        }
        $defined->{'@language'} = true;
      }

      // process all other keys
      foreach($ctx as $k => $v) {
        $this->_createTermDefinition($rval, $ctx, $k, $defined);
      }

      // cache result
      if(property_exists($jsonld_cache, 'activeCtx')) {
        $jsonld_cache->activeCtx->set($active_ctx, $ctx, $rval);
      }
    }

    return $rval;
  }

  /**
   * Expands a language map.
   *
   * @param stdClass $language_map the language map to expand.
   *
   * @return array the expanded language map.
   */
  protected function _expandLanguageMap($language_map) {
    $rval = array();
    $keys = array_keys((array)$language_map);
    sort($keys);
    foreach($keys as $key) {
      $values = $language_map->{$key};
      $values = self::arrayify($values);
      foreach($values as $item) {
        if($item === null) {
          continue;
        }
        if(!is_string($item)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; language map values must be strings.',
            'jsonld.SyntaxError', 'invalid language map value',
            array('languageMap', $language_map));
        }
        $rval[] = (object)array(
          '@value' => $item,
          '@language' => strtolower($key));
      }
    }
    return $rval;
  }

  /**
   * Labels the blank nodes in the given value using the given UniqueNamer.
   *
   * @param UniqueNamer $namer the UniqueNamer to use.
   * @param mixed $element the element with blank nodes to rename.
   *
   * @return mixed the element.
   */
  public function _labelBlankNodes($namer, $element) {
    if(is_array($element)) {
      $length = count($element);
      for($i = 0; $i < $length; ++$i) {
        $element[$i] = $this->_labelBlankNodes($namer, $element[$i]);
      }
    } else if(self::_isList($element)) {
      $element->{'@list'} = $this->_labelBlankNodes(
        $namer, $element->{'@list'});
    } else if(is_object($element)) {
      // rename blank node
      if(self::_isBlankNode($element)) {
        $name = null;
        if(property_exists($element, '@id')) {
          $name = $element->{'@id'};
        }
        $element->{'@id'} = $namer->getName($name);
      }

      // recursively apply to all keys
      $keys = array_keys((array)$element);
      sort($keys);
      foreach($keys as $key) {
        if($key !== '@id') {
          $element->{$key} = $this->_labelBlankNodes($namer, $element->{$key});
        }
      }
    }

    return $element;
  }

  /**
   * Expands the given value by using the coercion and keyword rules in the
   * given context.
   *
   * @param stdClass $active_ctx the active context to use.
   * @param string $active_property the property the value is associated with.
   * @param mixed $value the value to expand.
   *
   * @return mixed the expanded value.
   */
  protected function _expandValue($active_ctx, $active_property, $value) {
    // nothing to expand
    if($value === null) {
      return null;
    }

    // special-case expand @id and @type (skips '@id' expansion)
    $expanded_property = $this->_expandIri(
      $active_ctx, $active_property, array('vocab' => true));
    if($expanded_property === '@id') {
      return $this->_expandIri($active_ctx, $value, array('base' => true));
    } else if($expanded_property === '@type') {
      return $this->_expandIri(
        $active_ctx, $value, array('vocab' => true, 'base' => true));
    }

    // get type definition from context
    $type = self::getContextValue($active_ctx, $active_property, '@type');

    // do @id expansion (automatic for @graph)
    if($type === '@id' || ($expanded_property === '@graph' &&
      is_string($value))) {
      return (object)array('@id' => $this->_expandIri(
        $active_ctx, $value, array('base' => true)));
    }
    // do @id expansion w/vocab
    if($type === '@vocab') {
      return (object)array('@id' => $this->_expandIri(
        $active_ctx, $value, array('vocab' => true, 'base' => true)));
    }

    // do not expand keyword values
    if(self::_isKeyword($expanded_property)) {
      return $value;
    }

    $rval = new stdClass();

    // other type
    if($type !== null) {
      $rval->{'@type'} = $type;
    } else if(is_string($value)) {
      // check for language tagging for strings
      $language = self::getContextValue(
        $active_ctx, $active_property, '@language');
      if($language !== null) {
        $rval->{'@language'} = $language;
      }
    }
    $rval->{'@value'} = $value;

    return $rval;
  }

  /**
   * Creates an array of RDF triples for the given graph.
   *
   * @param stdClass $graph the graph to create RDF triples for.
   * @param UniqueNamer $namer for assigning bnode names.
   * @param assoc $options the RDF serialization options.
   *
   * @return array the array of RDF triples for the given graph.
   */
  protected function _graphToRDF($graph, $namer, $options) {
    $rval = array();

    $ids = array_keys((array)$graph);
    sort($ids);
    foreach($ids as $id) {
      $node = $graph->{$id};
      if($id === '"') {
        $id = '';
      }
      $properties = array_keys((array)$node);
      sort($properties);
      foreach($properties as $property) {
        $items = $node->{$property};
        if($property === '@type') {
          $property = self::RDF_TYPE;
        } else if(self::_isKeyword($property)) {
          continue;
        }

        foreach($items as $item) {
          // skip relative IRI subjects and predicates
          if(!(self::_isAbsoluteIri($id) && self::_isAbsoluteIri($property))) {
            continue;
          }

          // RDF subject
          $subject = new stdClass();
          $subject->type = (strpos($id, '_:') === 0) ? 'blank node' : 'IRI';
          $subject->value = $id;

          // RDF predicate
          $predicate = new stdClass();
          $predicate->type = (strpos($property, '_:') === 0 ?
            'blank node' : 'IRI');
          $predicate->value = $property;

          // skip bnode predicates unless producing generalized RDF
          if($predicate->type === 'blank node' &&
            !$options['produceGeneralizedRdf']) {
            continue;
          }

          if(self::_isList($item)) {
            // convert @list to triples
            $this->_listToRDF(
              $item->{'@list'}, $namer, $subject, $predicate, $rval);
          } else {
            // convert value or node object to triple
            $object = $this->_objectToRDF($item);
            // skip null objects (they are relative IRIs)
            if($object) {
              $rval[] = (object)array(
                'subject' => $subject,
                'predicate' => $predicate,
                'object' => $object);
            }
          }
        }
      }
    }

    return $rval;
  }

  /**
   * Converts a @list value into linked list of blank node RDF triples
   * (an RDF collection).
   *
   * @param array $list the @list value.
   * @param UniqueNamer $namer for assigning blank node names.
   * @param stdClass $subject the subject for the head of the list.
   * @param stdClass $predicate the predicate for the head of the list.
   * @param &array $triples the array of triples to append to.
   */
  protected function _listToRDF(
    $list, $namer, $subject, $predicate, &$triples) {
    $first = (object)array('type' => 'IRI', 'value' => self::RDF_FIRST);
    $rest = (object)array('type' => 'IRI', 'value' => self::RDF_REST);
    $nil = (object)array('type' => 'IRI', 'value' => self::RDF_NIL);

    foreach($list as $item) {
      $blank_node = (object)array(
        'type' => 'blank node', 'value' => $namer->getName());
      $triples[] = (object)array(
        'subject' => $subject,
        'predicate' => $predicate,
        'object' => $blank_node);

      $subject = $blank_node;
      $predicate = $first;
      $object = $this->_objectToRDF($item);
      // skip null objects (they are relative IRIs)
      if($object) {
        $triples[] = (object)array(
          'subject' => $subject,
          'predicate' => $predicate,
          'object' => $object);
      }

      $predicate = $rest;
    }

    $triples[] = (object)array(
      'subject' => $subject, 'predicate' => $predicate, 'object' => $nil);
  }

  /**
   * Converts a JSON-LD value object to an RDF literal or a JSON-LD string or
   * node object to an RDF resource.
   *
   * @param mixed $item the JSON-LD value or node object.
   *
   * @return stdClass the RDF literal or RDF resource.
   */
  protected function _objectToRDF($item) {
    $object = new stdClass();

    if(self::_isValue($item)) {
      $object->type = 'literal';
      $value = $item->{'@value'};
      $datatype = property_exists($item, '@type') ? $item->{'@type'} : null;

      // convert to XSD datatypes as appropriate
      if(is_bool($value)) {
        $object->value = ($value ? 'true' : 'false');
        $object->datatype = $datatype ? $datatype : self::XSD_BOOLEAN;
      } else if(is_double($value) || $datatype == self::XSD_DOUBLE) {
        // canonical double representation
        $object->value = preg_replace(
          '/(\d)0*E\+?/', '$1E', sprintf('%1.15E', $value));
        $object->datatype = $datatype ? $datatype : self::XSD_DOUBLE;
      } else if(is_integer($value)) {
        $object->value = strval($value);
        $object->datatype = $datatype ? $datatype : self::XSD_INTEGER;
      } else if(property_exists($item, '@language')) {
        $object->value = $value;
        $object->datatype = $datatype ? $datatype : self::RDF_LANGSTRING;
        $object->language = $item->{'@language'};
      } else {
        $object->value = $value;
        $object->datatype = $datatype ? $datatype : self::XSD_STRING;
      }
    } else {
      // convert string/node object to RDF
      $id = is_object($item) ? $item->{'@id'} : $item;
      $object->type = (strpos($id, '_:') === 0) ? 'blank node' : 'IRI';
      $object->value = $id;
    }

    // skip relative IRIs
    if($object->type === 'IRI' && !self::_isAbsoluteIri($object->value)) {
      return null;
    }

    return $object;
  }

  /**
   * Converts an RDF triple object to a JSON-LD object.
   *
   * @param stdClass $o the RDF triple object to convert.
   * @param bool $use_native_types true to output native types, false not to.
   *
   * @return stdClass the JSON-LD object.
   */
  protected function _RDFToObject($o, $use_native_types) {
    // convert IRI/blank node object to JSON-LD
    if($o->type === 'IRI' || $o->type === 'blank node') {
      return (object)array('@id' => $o->value);
    }

    // convert literal object to JSON-LD
    $rval = (object)array('@value' => $o->value);

    if(property_exists($o, 'language')) {
      // add language
      $rval->{'@language'} = $o->language;
    } else {
      // add datatype
      $type = $o->datatype;
      // use native types for certain xsd types
      if($use_native_types) {
        if($type === self::XSD_BOOLEAN) {
          if($rval->{'@value'} === 'true') {
            $rval->{'@value'} = true;
          } else if($rval->{'@value'} === 'false') {
            $rval->{'@value'} = false;
          }
        } else if(is_numeric($rval->{'@value'})) {
          if($type === self::XSD_INTEGER) {
            $i = intval($rval->{'@value'});
            if(strval($i) === $rval->{'@value'}) {
              $rval->{'@value'} = $i;
            }
          } else if($type === self::XSD_DOUBLE) {
            $rval->{'@value'} = doubleval($rval->{'@value'});
          }
        }
        // do not add native type
        if(!in_array($type, array(
          self::XSD_BOOLEAN, self::XSD_INTEGER, self::XSD_DOUBLE,
          self::XSD_STRING))) {
          $rval->{'@type'} = $type;
        }
      } else if($type !== self::XSD_STRING) {
        $rval->{'@type'} = $type;
      }
    }

    return $rval;
  }

  /**
   * Recursively flattens the subjects in the given JSON-LD expanded input
   * into a node map.
   *
   * @param mixed $input the JSON-LD expanded input.
   * @param stdClass $graphs a map of graph name to subject map.
   * @param string $graph the name of the current graph.
   * @param UniqueNamer $namer the blank node namer.
   * @param mixed $name the name assigned to the current input if it is a bnode.
   * @param mixed $list the list to append to, null for none.
   */
  protected function _createNodeMap(
    $input, $graphs, $graph, $namer, $name=null, $list=null) {
    // recurse through array
    if(is_array($input)) {
      foreach($input as $e) {
        $this->_createNodeMap($e, $graphs, $graph, $namer, null, $list);
      }
      return;
    }

    // add non-object to list
    if(!is_object($input)) {
      if($list !== null) {
        $list[] = $input;
      }
      return;
    }

    // add values to list
    if(self::_isValue($input)) {
      if(property_exists($input, '@type')) {
        $type = $input->{'@type'};
        // rename @type blank node
        if(strpos($type, '_:') === 0) {
          $type = $input->{'@type'} = $namer->getName($type);
        }
      }
      if($list !== null) {
        $list[] = $input;
      }
      return;
    }

    // Note: At this point, input must be a subject.

    // spec requires @type to be named first, so assign names early
    if(property_exists($input, '@type')) {
      foreach($input->{'@type'} as $type) {
        if(strpos($type, '_:') === 0) {
          $namer->getName($type);
        }
      }
    }

    // get name for subject
    if($name === null) {
      if(property_exists($input, '@id')) {
        $name = $input->{'@id'};
      }
      if(self::_isBlankNode($input)) {
        $name = $namer->getName($name);
      }
    }

    // add subject reference to list
    if($list !== null) {
      $list[] = (object)array('@id' => $name);
    }

    // create new subject or merge into existing one
    if(!property_exists($graphs, $graph)) {
      $graphs->{$graph} = new stdClass();
    }
    $subjects = $graphs->{$graph};
    if(!property_exists($subjects, $name)) {
      if($name === '') {
        $subjects->{'"'} = new stdClass();
      } else {
        $subjects->{$name} = new stdClass();
      }
    }
    if($name === '') {
      $subject = $subjects->{'"'};
    } else {
      $subject = $subjects->{$name};
    }
    $subject->{'@id'} = $name;
    $properties = array_keys((array)$input);
    sort($properties);
    foreach($properties as $property) {
      // skip @id
      if($property === '@id') {
        continue;
      }

      // handle reverse properties
      if($property === '@reverse') {
        $referenced_node = (object)array('@id' => $name);
        $reverse_map = $input->{'@reverse'};
        foreach($reverse_map as $reverse_property => $items) {
          foreach($items as $item) {
            $item_name = null;
            if(property_exists($item, '@id')) {
              $item_name = $item->{'@id'};
            }
            if(self::_isBlankNode($item)) {
              $item_name = $namer->getName($item_name);
            }
            $this->_createNodeMap($item, $graphs, $graph, $namer, $item_name);
            if($item_name === '') {
              $item_name = '"';
            }
            self::addValue(
              $subjects->{$item_name}, $reverse_property, $referenced_node,
              array('propertyIsArray' => true, 'allowDuplicate' => false));
          }
        }
        continue;
      }

      // recurse into graph
      if($property === '@graph') {
        // add graph subjects map entry
        if(!property_exists($graphs, $name)) {
          // FIXME: temporary hack to avoid empty property bug
          if(!$name) {
            $name = '"';
          }
          $graphs->{$name} = new stdClass();
        }
        $g = ($graph === '@merged') ? $graph : $name;
        $this->_createNodeMap(
          $input->{$property}, $graphs, $g, $namer, null, null);
        continue;
      }

      // copy non-@type keywords
      if($property !== '@type' && self::_isKeyword($property)) {
        if($property === '@index' && property_exists($subject, '@index') &&
          ($input->{'@index'} !== $subject->{'@index'} ||
          $input->{'@index'}->{'@id'} !== $subject->{'@index'}->{'@id'})) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; conflicting @index property detected.',
            'jsonld.SyntaxError', 'conflicting indexes',
            array('subject' => $subject));
        }
        $subject->{$property} = $input->{$property};
        continue;
      }

      // iterate over objects
      $objects = $input->{$property};

      // if property is a bnode, assign it a new id
      if(strpos($property, '_:') === 0) {
        $property = $namer->getName($property);
      }

      // ensure property is added for empty arrays
      if(count($objects) === 0) {
        self::addValue(
          $subject, $property, array(), array('propertyIsArray' => true));
        continue;
      }
      foreach($objects as $o) {
        if($property === '@type') {
          // rename @type blank nodes
          $o = (strpos($o, '_:') === 0) ? $namer->getName($o) : $o;
        }

        // handle embedded subject or subject reference
        if(self::_isSubject($o) || self::_isSubjectReference($o)) {
          // rename blank node @id
          $id = property_exists($o, '@id') ? $o->{'@id'} : null;
          if(self::_isBlankNode($o)) {
            $id = $namer->getName($id);
          }

          // add reference and recurse
          self::addValue(
            $subject, $property, (object)array('@id' => $id),
            array('propertyIsArray' => true, 'allowDuplicate' => false));
          $this->_createNodeMap($o, $graphs, $graph, $namer, $id, null);
        } else if(self::_isList($o)) {
          // handle @list
          $_list = new ArrayObject();
          $this->_createNodeMap(
            $o->{'@list'}, $graphs, $graph, $namer, $name, $_list);
          $o = (object)array('@list' => (array)$_list);
          self::addValue(
            $subject, $property, $o,
            array('propertyIsArray' => true, 'allowDuplicate' => false));
        } else {
          // handle @value
          $this->_createNodeMap($o, $graphs, $graph, $namer, $name, null);
          self::addValue(
            $subject, $property, $o,
            array('propertyIsArray' => true, 'allowDuplicate' => false));
        }
      }
    }
  }

  /**
   * Frames subjects according to the given frame.
   *
   * @param stdClass $state the current framing state.
   * @param array $subjects the subjects to filter.
   * @param array $frame the frame.
   * @param mixed $parent the parent subject or top-level array.
   * @param mixed $property the parent property, initialized to null.
   */
  protected function _matchFrame(
    $state, $subjects, $frame, $parent, $property) {
    // validate the frame
    $this->_validateFrame($frame);
    $frame = $frame[0];

    // get flags for current frame
    $options = $state->options;
    $flags = array(
      'embed' => $this->_getFrameFlag($frame, $options, 'embed'),
      'explicit' => $this->_getFrameFlag($frame, $options, 'explicit'),
      'requireAll' => $this->_getFrameFlag($frame, $options, 'requireAll'));

    // filter out subjects that match the frame
    $matches = $this->_filterSubjects($state, $subjects, $frame, $flags);

    // add matches to output
    foreach($matches as $id => $subject) {
      if($flags['embed'] === '@link' && property_exists($state->link, $id)) {
        // TODO: may want to also match an existing linked subject against
        // the current frame ... so different frames could produce different
        // subjects that are only shared in-memory when the frames are the same

        // add existing linked subject
        $this->_addFrameOutput($parent, $property, $state->link->{$id});
        continue;
      }

      /* Note: In order to treat each top-level match as a compartmentalized
      result, clear the unique embedded subjects map when the property is null,
      which only occurs at the top-level. */
      if($property === null) {
        $state->uniqueEmbeds = new stdClass();
      }

      // start output for subject
      $output = new stdClass();
      $output->{'@id'} = $id;
      $state->link->{$id} = $output;

      // if embed is @never or if a circular reference would be created by an
      // embed, the subject cannot be embedded, just add the reference;
      // note that a circular reference won't occur when the embed flag is
      // `@link` as the above check will short-circuit before reaching this point
      if($flags['embed'] === '@never' ||
        $this->_createsCircularReference($subject, $state->subjectStack)) {
        $this->_addFrameOutput($parent, $property, $output);
        continue;
      }

      // if only the last match should be embedded
      if($flags['embed'] === '@last') {
        // remove any existing embed
        if(property_exists($state->uniqueEmbeds, $id)) {
          $this->_removeEmbed($state, $id);
        }
        $state->uniqueEmbeds->{$id} = array(
          'parent' => $parent, 'property' => $property);
      }

      // push matching subject onto stack to enable circular embed checks
      $state->subjectStack[] = $subject;

      // iterate over subject properties
      $props = array_keys((array)$subject);
      sort($props);
      foreach($props as $prop) {
        // copy keywords to output
        if(self::_isKeyword($prop)) {
          $output->{$prop} = self::copy($subject->{$prop});
          continue;
        }

        // explicit is on and property isn't in the frame, skip processing
        if($flags['explicit'] && !property_exists($frame, $prop)) {
          continue;
        }

        // add objects
        $objects = $subject->{$prop};
        foreach($objects as $o) {
          // recurse into list
          if(self::_isList($o)) {
            // add empty list
            $list = (object)array('@list' => array());
            $this->_addFrameOutput($output, $prop, $list);

            // add list objects
            $src = $o->{'@list'};
            foreach($src as $o) {
              if(self::_isSubjectReference($o)) {
                // recurse into subject reference
                $subframe = (property_exists($frame, $prop) ?
                  $frame->{$prop}[0]->{'@list'} :
                  $this->_createImplicitFrame($flags));
                $this->_matchFrame(
                  $state, array($o->{'@id'}), $subframe, $list, '@list');
              } else {
                // include other values automatically
                $this->_addFrameOutput($list, '@list', self::copy($o));
              }
            }
            continue;
          }

          if(self::_isSubjectReference($o)) {
            // recurse into subject reference
            $subframe = (property_exists($frame, $prop) ?
              $frame->{$prop} : $this->_createImplicitFrame($flags));
            $this->_matchFrame(
              $state, array($o->{'@id'}), $subframe, $output, $prop);
          } else {
            // include other values automatically
            $this->_addFrameOutput($output, $prop, self::copy($o));
          }
        }
      }

      // handle defaults
      $props = array_keys((array)$frame);
      sort($props);
      foreach($props as $prop) {
        // skip keywords
        if(self::_isKeyword($prop)) {
          continue;
        }

        // if omit default is off, then include default values for properties
        // that appear in the next frame but are not in the matching subject
        $next = $frame->{$prop}[0];
        $omit_default_on = $this->_getFrameFlag(
          $next, $options, 'omitDefault');
        if(!$omit_default_on && !property_exists($output, $prop)) {
          $preserve = '@null';
          if(property_exists($next, '@default')) {
            $preserve = self::copy($next->{'@default'});
          }
          $preserve = self::arrayify($preserve);
          $output->{$prop} = array((object)array('@preserve' => $preserve));
        }
      }

      // add output to parent
      $this->_addFrameOutput($parent, $property, $output);

      // pop matching subject from circular ref-checking stack
      array_pop($state->subjectStack);
    }
  }

  /**
   * Creates an implicit frame when recursing through subject matches. If
   * a frame doesn't have an explicit frame for a particular property, then
   * a wildcard child frame will be created that uses the same flags that the
   * parent frame used.
   *
   * @param assoc flags the current framing flags.
   *
   * @return array the implicit frame.
   */
  function _createImplicitFrame($flags) {
    $frame = new stdClass();
    foreach($flags as $key => $value) {
      $frame->{'@' . $key} = array($flags[$key]);
    }
    return array($frame);
  }

  /**
   * Checks the current subject stack to see if embedding the given subject
   * would cause a circular reference.
   *
   * @param stdClass subject_to_embed the subject to embed.
   * @param assoc subject_stack the current stack of subjects.
   *
   * @return bool true if a circular reference would be created, false if not.
   */
  function _createsCircularReference($subject_to_embed, $subject_stack) {
    for($i = count($subject_stack) - 1; $i >= 0; --$i) {
      if($subject_stack[$i]->{'@id'} === $subject_to_embed->{'@id'}) {
        return true;
      }
    }
    return false;
  }

  /**
   * Gets the frame flag value for the given flag name.
   *
   * @param stdClass $frame the frame.
   * @param stdClass $options the framing options.
   * @param string $name the flag name.
   *
   * @return mixed $the flag value.
   */
  protected function _getFrameFlag($frame, $options, $name) {
    $flag = "@$name";
    $rval = (property_exists($frame, $flag) ?
      $frame->{$flag}[0] : $options[$name]);
    if($name === 'embed') {
      // default is "@last"
      // backwards-compatibility support for "embed" maps:
      // true => "@last"
      // false => "@never"
      if($rval === true) {
        $rval = '@last';
      } else if($rval === false) {
        $rval = '@never';
      } else if($rval !== '@always' && $rval !== '@never' &&
        $rval !== '@link') {
        $rval = '@last';
      }
    }
    return $rval;
  }

  /**
   * Validates a JSON-LD frame, throwing an exception if the frame is invalid.
   *
   * @param array $frame the frame to validate.
   */
  protected function _validateFrame($frame) {
    if(!is_array($frame) || count($frame) !== 1 || !is_object($frame[0])) {
      throw new JsonLdException(
        'Invalid JSON-LD syntax; a JSON-LD frame must be a single object.',
        'jsonld.SyntaxError', null, array('frame' => $frame));
    }
  }

  /**
   * Returns a map of all of the subjects that match a parsed frame.
   *
   * @param stdClass $state the current framing state.
   * @param array $subjects the set of subjects to filter.
   * @param stdClass $frame the parsed frame.
   * @param assoc $flags the frame flags.
   *
   * @return stdClass all of the matched subjects.
   */
  protected function _filterSubjects($state, $subjects, $frame, $flags) {
    $rval = new stdClass();
    sort($subjects);
    foreach($subjects as $id) {
      $subject = $state->subjects->{$id};
      if($this->_filterSubject($subject, $frame, $flags)) {
        $rval->{$id} = $subject;
      }
    }
    return $rval;
  }

  /**
   * Returns true if the given subject matches the given frame.
   *
   * @param stdClass $subject the subject to check.
   * @param stdClass $frame the frame to check.
   * @param assoc $flags the frame flags.
   *
   * @return bool true if the subject matches, false if not.
   */
  protected function _filterSubject($subject, $frame, $flags) {
    // check @type (object value means 'any' type, fall through to ducktyping)
    if(property_exists($frame, '@type') &&
      !(count($frame->{'@type'}) === 1 && is_object($frame->{'@type'}[0]))) {
      $types = $frame->{'@type'};
      foreach($types as $type) {
        // any matching @type is a match
        if(self::hasValue($subject, '@type', $type)) {
          return true;
        }
      }
      return false;
    }

    // check ducktype
    $wildcard = true;
    $matches_some = false;
    foreach($frame as $k => $v) {
      if(self::_isKeyword($k)) {
        // skip non-@id and non-@type
        if($k !== '@id' && $k !== '@type') {
          continue;
        }
        $wildcard = false;

        // check @id for a specific @id value
        if($k === '@id' && is_string($v)) {
          if(!property_exists($subject, $k) || $subject->{$k} !== $v) {
            return false;
          }
          $matches_some = true;
          continue;
        }
      }

      $wildcard = false;

      if(property_exists($subject, $k)) {
        // $v === [] means do not match if property is present
        if(is_array($v) && count($v) === 0) {
          return false;
        }
        $matches_some = true;
        continue;
      }

      // all properties must match to be a duck unless a @default is specified
      $has_default = (is_array($v) && count($v) === 1 && is_object($v[0]) &&
        property_exists($v[0], '@default'));
      if($flags['requireAll'] && !$has_default) {
        return false;
      }
    }

    // return true if wildcard or subject matches some properties
    return $wildcard || $matches_some;
  }

  /**
   * Removes an existing embed.
   *
   * @param stdClass $state the current framing state.
   * @param string $id the @id of the embed to remove.
   */
  protected function _removeEmbed($state, $id) {
    // get existing embed
    $embeds = $state->uniqueEmbeds;
    $embed = $embeds->{$id};
    $property = $embed['property'];

    // create reference to replace embed
    $subject = (object)array('@id' => $id);

    // remove existing embed
    if(is_array($embed->parent)) {
      // replace subject with reference
      foreach($embed->parent as $i => $parent) {
        if(self::compareValues($parent, $subject)) {
          $embed->parent[$i] = $subject;
          break;
        }
      }
    } else {
      // replace subject with reference
      $use_array = is_array($embed->parent->{$property});
      self::removeValue($embed->parent, $property, $subject,
        array('propertyIsArray' => $use_array));
      self::addValue($embed->parent, $property, $subject,
        array('propertyIsArray' => $use_array));
    }

    // recursively remove dependent dangling embeds
    $removeDependents = function($id) {
      // get embed keys as a separate array to enable deleting keys in map
      $ids = array_keys((array)$embeds);
      foreach($ids as $next) {
        if(property_exists($embeds, $next) &&
          is_object($embeds->{$next}->parent) &&
          $embeds->{$next}->parent->{'@id'} === $id) {
          unset($embeds->{$next});
          $removeDependents($next);
        }
      }
    };
    $removeDependents($id);
  }

  /**
   * Adds framing output to the given parent.
   *
   * @param mixed $parent the parent to add to.
   * @param string $property the parent property.
   * @param mixed $output the output to add.
   */
  protected function _addFrameOutput($parent, $property, $output) {
    if(is_object($parent) && !($parent instanceof ArrayObject)) {
      self::addValue(
        $parent, $property, $output, array('propertyIsArray' => true));
    } else {
      $parent[] = $output;
    }
  }

  /**
   * Removes the @preserve keywords as the last step of the framing algorithm.
   *
   * @param stdClass $ctx the active context used to compact the input.
   * @param mixed $input the framed, compacted output.
   * @param assoc $options the compaction options used.
   *
   * @return mixed the resulting output.
   */
  protected function _removePreserve($ctx, $input, $options) {
    // recurse through arrays
    if(is_array($input)) {
      $output = array();
      foreach($input as $e) {
        $result = $this->_removePreserve($ctx, $e, $options);
        // drop nulls from arrays
        if($result !== null) {
          $output[] = $result;
        }
      }
      $input = $output;
    } else if(is_object($input)) {
      // remove @preserve
      if(property_exists($input, '@preserve')) {
        if($input->{'@preserve'} === '@null') {
          return null;
        }
        return $input->{'@preserve'};
      }

      // skip @values
      if(self::_isValue($input)) {
        return $input;
      }

      // recurse through @lists
      if(self::_isList($input)) {
        $input->{'@list'} = $this->_removePreserve(
          $ctx, $input->{'@list'}, $options);
        return $input;
      }

      // handle in-memory linked nodes
      $id_alias = $this->_compactIri($ctx, '@id');
      if(property_exists($input, $id_alias)) {
        $id = $input->{$id_alias};
        if(isset($options['link'][$id])) {
          $idx = array_search($input, $options['link'][$id]);
          if($idx === false) {
            // prevent circular visitation
            $options['link'][$id][] = $input;
          } else {
            // already visited
            return $options['link'][$id][$idx];
          }
        } else {
          // prevent circular visitation
          $options['link'][$id] = array($input);
        }
      }

      // recurse through properties
      foreach($input as $prop => $v) {
        $result = $this->_removePreserve($ctx, $v, $options);
        $container = self::getContextValue($ctx, $prop, '@container');
        if($options['compactArrays'] &&
          is_array($result) && count($result) === 1 &&
          $container !== '@set' && $container !== '@list') {
          $result = $result[0];
        }
        $input->{$prop} = $result;
      }
    }
    return $input;
  }

  /**
   * Compares two RDF triples for equality.
   *
   * @param stdClass $t1 the first triple.
   * @param stdClass $t2 the second triple.
   *
   * @return true if the triples are the same, false if not.
   */
  protected static function _compareRDFTriples($t1, $t2) {
    foreach(array('subject', 'predicate', 'object') as $attr) {
      if($t1->{$attr}->type !== $t2->{$attr}->type ||
        $t1->{$attr}->value !== $t2->{$attr}->value) {
        return false;
      }
    }
    if(property_exists($t1->object, 'language') !==
      property_exists($t1->object, 'language')) {
      return false;
    }
    if(property_exists($t1->object, 'language') &&
      $t1->object->language !== $t2->object->language) {
      return false;
    }
    if(property_exists($t1->object, 'datatype') &&
      $t1->object->datatype !== $t2->object->datatype) {
      return false;
    }
    return true;
  }

  /**
   * Hashes all of the quads about a blank node.
   *
   * @param string $id the ID of the bnode to hash quads for.
   * @param stdClass $bnodes the mapping of bnodes to quads.
   * @param UniqueNamer $namer the canonical bnode namer.
   *
   * @return string the new hash.
   */
  protected function _hashQuads($id, $bnodes, $namer) {
    // return cached hash
    if(property_exists($bnodes->{$id}, 'hash')) {
      return $bnodes->{$id}->hash;
    }

    // serialize all of bnode's quads
    $quads = $bnodes->{$id}->quads;
    $nquads = array();
    foreach($quads as $quad) {
      $nquads[] = $this->toNQuad($quad, property_exists($quad, 'name') ?
        $quad->name->value : null, $id);
    }

    // sort serialized quads
    sort($nquads);

    // cache and return hashed quads
    $hash = $bnodes->{$id}->hash = hash('sha256',implode($nquads));
    return $hash;
  }

  /**
   * Produces a hash for the paths of adjacent bnodes for a bnode,
   * incorporating all information about its subgraph of bnodes. This
   * method will recursively pick adjacent bnode permutations that produce the
   * lexicographically-least 'path' serializations.
   *
   * @param string $id the ID of the bnode to hash paths for.
   * @param stdClass $bnodes the map of bnode quads.
   * @param UniqueNamer $namer the canonical bnode namer.
   * @param UniqueNamer $path_namer the namer used to assign names to adjacent
   *          bnodes.
   *
   * @return stdClass the hash and path namer used.
   */
  protected function _hashPaths($id, $bnodes, $namer, $path_namer) {
    // create digest
    $md = hash_init('sha256');

    // group adjacent bnodes by hash, keep properties and references separate
    $groups = new stdClass();
    $quads = $bnodes->{$id}->quads;
    foreach($quads as $quad) {
      // get adjacent bnode
      $bnode = $this->_getAdjacentBlankNodeName($quad->subject, $id);
      if($bnode !== null) {
        // normal property
        $direction = 'p';
      } else {
        $bnode = $this->_getAdjacentBlankNodeName($quad->object, $id);
        if($bnode !== null) {
          // reverse property
          $direction = 'r';
        }
      }
      if($bnode !== null) {
        // get bnode name (try canonical, path, then hash)
        if($namer->isNamed($bnode)) {
          $name = $namer->getName($bnode);
        } else if($path_namer->isNamed($bnode)) {
          $name = $path_namer->getName($bnode);
        } else {
          $name = $this->_hashQuads($bnode, $bnodes, $namer);
        }

        // hash direction, property, and bnode name/hash
        $group_md = hash_init('sha256');
        hash_update($group_md, $direction);
        hash_update($group_md, $quad->predicate->value);
        hash_update($group_md, $name);
        $group_hash = hash_final($group_md);

        // add bnode to hash group
        if(property_exists($groups, $group_hash)) {
          $groups->{$group_hash}[] = $bnode;
        } else {
          $groups->{$group_hash} = array($bnode);
        }
      }
    }

    // iterate over groups in sorted hash order
    $group_hashes = array_keys((array)$groups);
    sort($group_hashes);
    foreach($group_hashes as $group_hash) {
      // digest group hash
      hash_update($md, $group_hash);

      // choose a path and namer from the permutations
      $chosen_path = null;
      $chosen_namer = null;
      $permutator = new Permutator($groups->{$group_hash});
      while($permutator->hasNext()) {
        $permutation = $permutator->next();
        $path_namer_copy = clone $path_namer;

        // build adjacent path
        $path = '';
        $skipped = false;
        $recurse = array();
        foreach($permutation as $bnode) {
          // use canonical name if available
          if($namer->isNamed($bnode)) {
            $path .= $namer->getName($bnode);
          } else {
            // recurse if bnode isn't named in the path yet
            if(!$path_namer_copy->isNamed($bnode)) {
              $recurse[] = $bnode;
            }
            $path .= $path_namer_copy->getName($bnode);
          }

          // skip permutation if path is already >= chosen path
          if($chosen_path !== null && strlen($path) >= strlen($chosen_path) &&
            $path > $chosen_path) {
            $skipped = true;
            break;
          }
        }

        // recurse
        if(!$skipped) {
          foreach($recurse as $bnode) {
            $result = $this->_hashPaths(
              $bnode, $bnodes, $namer, $path_namer_copy);
            $path .= $path_namer_copy->getName($bnode);
            $path .= "<{$result->hash}>";
            $path_namer_copy = $result->pathNamer;

            // skip permutation if path is already >= chosen path
            if($chosen_path !== null &&
              strlen($path) >= strlen($chosen_path) && $path > $chosen_path) {
              $skipped = true;
              break;
            }
          }
        }

        if(!$skipped && ($chosen_path === null || $path < $chosen_path)) {
          $chosen_path = $path;
          $chosen_namer = $path_namer_copy;
        }
      }

      // digest chosen path and update namer
      hash_update($md, $chosen_path);
      $path_namer = $chosen_namer;
    }

    // return hash and path namer
    return (object)array(
      'hash' => hash_final($md), 'pathNamer' => $path_namer);
  }

  /**
   * A helper function that gets the blank node name from an RDF quad
   * node (subject or object). If the node is not a blank node or its
   * value does not match the given blank node ID, it will be returned.
   *
   * @param stdClass $node the RDF quad node.
   * @param string $id the ID of the blank node to look next to.
   *
   * @return mixed the adjacent blank node name or null if none was found.
   */
  protected function _getAdjacentBlankNodeName($node, $id) {
    if($node->type === 'blank node' && $node->value !== $id) {
      return $node->value;
    }
    return null;
  }

  /**
   * Compares two strings first based on length and then lexicographically.
   *
   * @param string $a the first string.
   * @param string $b the second string.
   *
   * @return integer -1 if a < b, 1 if a > b, 0 if a == b.
   */
  protected function _compareShortestLeast($a, $b) {
    $len_a = strlen($a);
    $len_b = strlen($b);
    if($len_a < $len_b) {
      return -1;
    }
    if($len_b < $len_a) {
      return 1;
    }
    if($a === $b) {
      return 0;
    }
    return ($a < $b) ? -1 : 1;
  }

  /**
   * Picks the preferred compaction term from the given inverse context entry.
   *
   * @param active_ctx the active context.
   * @param iri the IRI to pick the term for.
   * @param value the value to pick the term for.
   * @param containers the preferred containers.
   * @param type_or_language either '@type' or '@language'.
   * @param type_or_language_value the preferred value for '@type' or
   *          '@language'.
   *
   * @return mixed the preferred term.
   */
  protected function _selectTerm(
    $active_ctx, $iri, $value, $containers,
    $type_or_language, $type_or_language_value) {
    if($type_or_language_value === null) {
      $type_or_language_value = '@null';
    }

    // options for the value of @type or @language
    $prefs = array();

    // determine prefs for @id based on whether or not value compacts to a term
    if(($type_or_language_value === '@id' ||
      $type_or_language_value === '@reverse') &&
      self::_isSubjectReference($value)) {
      // prefer @reverse first
      if($type_or_language_value === '@reverse') {
        $prefs[] = '@reverse';
      }
      // try to compact value to a term
      $term = $this->_compactIri(
        $active_ctx, $value->{'@id'}, null, array('vocab' => true));
      if(property_exists($active_ctx->mappings, $term) &&
        $active_ctx->mappings->{$term} &&
        $active_ctx->mappings->{$term}->{'@id'} === $value->{'@id'}) {
        // prefer @vocab
        array_push($prefs, '@vocab', '@id');
      } else {
        // prefer @id
        array_push($prefs, '@id', '@vocab');
      }
    } else {
      $prefs[] = $type_or_language_value;
    }
    $prefs[] = '@none';

    $container_map = $active_ctx->inverse->{$iri};
    foreach($containers as $container) {
      // if container not available in the map, continue
      if(!property_exists($container_map, $container)) {
        continue;
      }

      $type_or_language_value_map =
        $container_map->{$container}->{$type_or_language};
      foreach($prefs as $pref) {
        // if type/language option not available in the map, continue
        if(!property_exists($type_or_language_value_map, $pref)) {
          continue;
        }

        // select term
        return $type_or_language_value_map->{$pref};
      }
    }
    return null;
  }

  /**
   * Compacts an IRI or keyword into a term or prefix if it can be. If the
   * IRI has an associated value it may be passed.
   *
   * @param stdClass $active_ctx the active context to use.
   * @param string $iri the IRI to compact.
   * @param mixed $value the value to check or null.
   * @param assoc $relative_to options for how to compact IRIs:
   *          vocab: true to split after @vocab, false not to.
   * @param bool $reverse true if a reverse property is being compacted, false
   *          if not.
   *
   * @return string the compacted term, prefix, keyword alias, or original IRI.
   */
  protected function _compactIri(
    $active_ctx, $iri, $value=null, $relative_to=array(), $reverse=false) {
    // can't compact null
    if($iri === null) {
      return $iri;
    }

    $inverse_ctx = $this->_getInverseContext($active_ctx);

    if(self::_isKeyword($iri)) {
      // a keyword can only be compacted to simple alias
      if(property_exists($inverse_ctx, $iri)) {
        return $inverse_ctx->$iri->{'@none'}->{'@type'}->{'@none'};
      }
      return $iri;
    }

    if(!isset($relative_to['vocab'])) {
      $relative_to['vocab'] = false;
    }

    // use inverse context to pick a term if iri is relative to vocab
    if($relative_to['vocab'] && property_exists($inverse_ctx, $iri)) {
      $default_language = '@none';
      if(property_exists($active_ctx, '@language')) {
        $default_language = $active_ctx->{'@language'};
      }

      // prefer @index if available in value
      $containers = array();
      if(is_object($value) && property_exists($value, '@index')) {
        $containers[] = '@index';
      }

      // defaults for term selection based on type/language
      $type_or_language = '@language';
      $type_or_language_value = '@null';

      if($reverse) {
        $type_or_language = '@type';
        $type_or_language_value = '@reverse';
        $containers[] = '@set';
      } else if(self::_isList($value)) {
        // choose the most specific term that works for all elements in @list
        // only select @list containers if @index is NOT in value
        if(!property_exists($value, '@index')) {
          $containers[] = '@list';
        }
        $list = $value->{'@list'};
        $common_language = (count($list) === 0) ? $default_language : null;
        $common_type = null;
        foreach($list as $item) {
          $item_language = '@none';
          $item_type = '@none';
          if(self::_isValue($item)) {
            if(property_exists($item, '@language')) {
              $item_language = $item->{'@language'};
            } else if(property_exists($item, '@type')) {
              $item_type = $item->{'@type'};
            } else {
              // plain literal
              $item_language = '@null';
            }
          } else {
            $item_type = '@id';
          }
          if($common_language === null) {
            $common_language = $item_language;
          } else if($item_language !== $common_language &&
            self::_isValue($item)) {
            $common_language = '@none';
          }
          if($common_type === null) {
            $common_type = $item_type;
          } else if($item_type !== $common_type) {
            $common_type = '@none';
          }
          // there are different languages and types in the list, so choose
          // the most generic term, no need to keep iterating the list
          if($common_language === '@none' && $common_type === '@none') {
            break;
          }
        }
        if($common_language === null) {
          $common_language = '@none';
        }
        if($common_type === null) {
          $common_type = '@none';
        }
        if($common_type !== '@none') {
          $type_or_language = '@type';
          $type_or_language_value = $common_type;
        } else {
          $type_or_language_value = $common_language;
        }
      } else {
        if(self::_isValue($value)) {
          if(property_exists($value, '@language') &&
            !property_exists($value, '@index')) {
            $containers[] = '@language';
            $type_or_language_value = $value->{'@language'};
          } else if(property_exists($value, '@type')) {
            $type_or_language = '@type';
            $type_or_language_value = $value->{'@type'};
          }
        } else {
          $type_or_language = '@type';
          $type_or_language_value = '@id';
        }
        $containers[] = '@set';
      }

      // do term selection
      $containers[] = '@none';
      $term = $this->_selectTerm(
        $active_ctx, $iri, $value,
        $containers, $type_or_language, $type_or_language_value);
      if($term !== null) {
        return $term;
      }
    }

    // no term match, use @vocab if available
    if($relative_to['vocab']) {
      if(property_exists($active_ctx, '@vocab')) {
        // determine if vocab is a prefix of the iri
        $vocab = $active_ctx->{'@vocab'};
        if(strpos($iri, $vocab) === 0 && $iri !== $vocab) {
          // use suffix as relative iri if it is not a term in the active
          // context
          $suffix = substr($iri, strlen($vocab));
          if(!property_exists($active_ctx->mappings, $suffix)) {
            return $suffix;
          }
        }
      }
    }

    // no term or @vocab match, check for possible CURIEs
    $choice = null;
    $idx = 0;
    $partial_matches = array();
    $iri_map = $active_ctx->fast_curie_map;
    // check for partial matches of against `iri`, which means look until
    // iri.length - 1, not full length
    $max_partial_length = strlen($iri) - 1;
    for(; $idx < $max_partial_length && isset($iri_map[$iri[$idx]]); ++$idx) {
      $iri_map = $iri_map[$iri[$idx]];
      if(isset($iri_map[''])) {
        $entry = $iri_map[''][0];
        $entry->iri_length = $idx + 1;
        $partial_matches[] = $entry;
      }
    }
    // check partial matches in reverse order to prefer longest ones first
    $partial_matches = array_reverse($partial_matches);
    foreach($partial_matches as $entry) {
      $terms = $entry->terms;
      foreach($terms as $term) {
        // a CURIE is usable if:
        // 1. it has no mapping, OR
        // 2. value is null, which means we're not compacting an @value, AND
        //   the mapping matches the IRI
        $curie = $term . ':' . substr($iri, $entry->iri_length);
        $is_usable_curie = (!property_exists($active_ctx->mappings, $curie) ||
          ($value === null &&
          $active_ctx->mappings->{$curie}->{'@id'} === $iri));

        // select curie if it is shorter or the same length but
        // lexicographically less than the current choice
        if($is_usable_curie && ($choice === null ||
          self::_compareShortestLeast($curie, $choice) < 0)) {
          $choice = $curie;
        }
      }
    }

    // return chosen curie
    if($choice !== null) {
      return $choice;
    }

    // compact IRI relative to base
    if(!$relative_to['vocab']) {
      return jsonld_remove_base($active_ctx->{'@base'}, $iri);
    }

    // return IRI as is
    return $iri;
  }

  /**
   * Performs value compaction on an object with '@value' or '@id' as the only
   * property.
   *
   * @param stdClass $active_ctx the active context.
   * @param string $active_property the active property that points to the
   *          value.
   * @param mixed $value the value to compact.
   *
   * @return mixed the compaction result.
   */
  protected function _compactValue($active_ctx, $active_property, $value) {
    // value is a @value
    if(self::_isValue($value)) {
      // get context rules
      $type = self::getContextValue($active_ctx, $active_property, '@type');
      $language = self::getContextValue(
        $active_ctx, $active_property, '@language');
      $container = self::getContextValue(
        $active_ctx, $active_property, '@container');

      // whether or not the value has an @index that must be preserved
      $preserve_index = (property_exists($value, '@index') &&
        $container !== '@index');

      // if there's no @index to preserve
      if(!$preserve_index) {
        // matching @type or @language specified in context, compact value
        if(self::_hasKeyValue($value, '@type', $type) ||
          self::_hasKeyValue($value, '@language', $language)) {
          return $value->{'@value'};
        }
      }

      // return just the value of @value if all are true:
      // 1. @value is the only key or @index isn't being preserved
      // 2. there is no default language or @value is not a string or
      //   the key has a mapping with a null @language
      $key_count = count(array_keys((array)$value));
      $is_value_only_key = ($key_count === 1 ||
        ($key_count === 2 && property_exists($value, '@index') &&
        !$preserve_index));
      $has_default_language = property_exists($active_ctx, '@language');
      $is_value_string = is_string($value->{'@value'});
      $has_null_mapping = (
        property_exists($active_ctx->mappings, $active_property) &&
        $active_ctx->mappings->{$active_property} !== null &&
        self::_hasKeyValue(
          $active_ctx->mappings->{$active_property}, '@language', null));
      if($is_value_only_key &&
        (!$has_default_language || !$is_value_string || $has_null_mapping)) {
        return $value->{'@value'};
      }

      $rval = new stdClass();

      // preserve @index
      if($preserve_index) {
        $rval->{$this->_compactIri($active_ctx, '@index')} = $value->{'@index'};
      }

      // compact @type IRI
      if(property_exists($value, '@type')) {
        $rval->{$this->_compactIri($active_ctx, '@type')} = $this->_compactIri(
          $active_ctx, $value->{'@type'}, null, array('vocab' => true));
      } else if(property_exists($value, '@language')) {
        // alias @language
        $rval->{$this->_compactIri($active_ctx, '@language')} =
          $value->{'@language'};
      }

      // alias @value
      $rval->{$this->_compactIri($active_ctx, '@value')} = $value->{'@value'};

      return $rval;
    }

    // value is a subject reference
    $expanded_property = $this->_expandIri(
      $active_ctx, $active_property, array('vocab' => true));
    $type = self::getContextValue($active_ctx, $active_property, '@type');
    $compacted = $this->_compactIri(
      $active_ctx, $value->{'@id'}, null,
      array('vocab' => ($type === '@vocab')));

    // compact to scalar
    if($type === '@id' || $type === '@vocab' ||
      $expanded_property === '@graph') {
      return $compacted;
    }

    $rval = (object)array(
      $this->_compactIri($active_ctx, '@id') => $compacted);
    return $rval;
  }

  /**
   * Creates a term definition during context processing.
   *
   * @param stdClass $active_ctx the current active context.
   * @param stdClass $local_ctx the local context being processed.
   * @param string $term the key in the local context to define the mapping for.
   * @param stdClass $defined a map of defining/defined keys to detect cycles
   *          and prevent double definitions.
   */
  protected function _createTermDefinition(
    $active_ctx, $local_ctx, $term, $defined) {
    if(property_exists($defined, $term)) {
      // term already defined
      if($defined->{$term}) {
        return;
      }
      // cycle detected
      throw new JsonLdException(
        'Cyclical context definition detected.',
        'jsonld.CyclicalContext', 'cyclic IRI mapping',
        array('context' => $local_ctx, 'term' => $term));
    }

    // now defining term
    $defined->{$term} = false;

    if(self::_isKeyword($term)) {
      throw new JsonLdException(
        'Invalid JSON-LD syntax; keywords cannot be overridden.',
        'jsonld.SyntaxError', 'keyword redefinition',
        array('context' => $local_ctx, 'term' => $term));
    }

    // remove old mapping
    if(property_exists($active_ctx->mappings, $term)) {
      unset($active_ctx->mappings->{$term});
    }

    // get context term value
    $value = $local_ctx->{$term};

    // clear context entry
    if($value === null || (is_object($value) &&
      self::_hasKeyValue($value, '@id', null))) {
      $active_ctx->mappings->{$term} = null;
      $defined->{$term} = true;
      return;
    }

    // convert short-hand value to object w/@id
    if(is_string($value)) {
      $value = (object)array('@id' => $value);
    }

    if(!is_object($value)) {
      throw new JsonLdException(
        'Invalid JSON-LD syntax; @context property values must be ' .
        'strings or objects.', 'jsonld.SyntaxError', 'invalid term definition',
        array('context' => $local_ctx));
    }

    // create new mapping
    $mapping = $active_ctx->mappings->{$term} = new stdClass();
    $mapping->reverse = false;

    if(property_exists($value, '@reverse')) {
      if(property_exists($value, '@id')) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; a @reverse term definition must not ' +
          'contain @id.', 'jsonld.SyntaxError', 'invalid reverse property',
          array('context' => $local_ctx));
      }
      $reverse = $value->{'@reverse'};
      if(!is_string($reverse)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; a @context @reverse value must be a string.',
          'jsonld.SyntaxError', 'invalid IRI mapping',
          array('context' => $local_ctx));
      }

      // expand and add @id mapping
      $id = $this->_expandIri(
        $active_ctx, $reverse, array('vocab' => true, 'base' => false),
        $local_ctx, $defined);
      if(!self::_isAbsoluteIri($id)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @reverse value must be ' .
          'an absolute IRI or a blank node identifier.',
          'jsonld.SyntaxError', 'invalid IRI mapping',
          array('context' => $local_ctx));
      }
      $mapping->{'@id'} = $id;
      $mapping->reverse = true;
    } else if(property_exists($value, '@id')) {
      $id = $value->{'@id'};
      if(!is_string($id)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @id value must be a string.',
          'jsonld.SyntaxError', 'invalid IRI mapping',
          array('context' => $local_ctx));
      }
      if($id !== $term) {
        // add @id to mapping
        $id = $this->_expandIri(
          $active_ctx, $id, array('vocab' => true, 'base' => false),
          $local_ctx, $defined);
        if(!self::_isAbsoluteIri($id) && !self::_isKeyword($id)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; @context @id value must be an ' .
            'absolute IRI, a blank node identifier, or a keyword.',
            'jsonld.SyntaxError', 'invalid IRI mapping',
            array('context' => $local_ctx));
        }
        $mapping->{'@id'} = $id;
      }
    }

    // always compute whether term has a colon as an optimization for
    // _compactIri
    $colon = strpos($term, ':');
    $mapping->_term_has_colon = ($colon !== false);

    if(!property_exists($mapping, '@id')) {
      // see if the term has a prefix
      if($mapping->_term_has_colon) {
        $prefix = substr($term, 0, $colon);
        if(property_exists($local_ctx, $prefix)) {
          // define parent prefix
          $this->_createTermDefinition(
            $active_ctx, $local_ctx, $prefix, $defined);
        }

        if(property_exists($active_ctx->mappings, $prefix) &&
          $active_ctx->mappings->{$prefix}) {
          // set @id based on prefix parent
          $suffix = substr($term, $colon + 1);
          $mapping->{'@id'} = $active_ctx->mappings->{$prefix}->{'@id'} .
            $suffix;
        } else {
          // term is an absolute IRI
          $mapping->{'@id'} = $term;
        }
      } else {
        // non-IRIs *must* define @ids if @vocab is not available
        if(!property_exists($active_ctx, '@vocab')) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; @context terms must define an @id.',
            'jsonld.SyntaxError', 'invalid IRI mapping',
            array('context' => $local_ctx, 'term' => $term));
        }
        // prepend vocab to term
        $mapping->{'@id'} = $active_ctx->{'@vocab'} . $term;
      }
    }

    // optimization to store length of @id once for _compactIri
    $mapping->_id_length = strlen($mapping->{'@id'});

    // IRI mapping now defined
    $defined->{$term} = true;

    if(property_exists($value, '@type')) {
      $type = $value->{'@type'};
      if(!is_string($type)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @type values must be strings.',
          'jsonld.SyntaxError', 'invalid type mapping',
          array('context' => $local_ctx));
      }

      if($type !== '@id' && $type !== '@vocab') {
        // expand @type to full IRI
        $type = $this->_expandIri(
          $active_ctx, $type, array('vocab' => true), $local_ctx, $defined);
        if(!self::_isAbsoluteIri($type)) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; an @context @type value must ' .
            'be an absolute IRI.', 'jsonld.SyntaxError',
            'invalid type mapping', array('context' => $local_ctx));
        }
        if(strpos($type, '_:') === 0) {
          throw new JsonLdException(
            'Invalid JSON-LD syntax; an @context @type values must ' .
            'be an IRI, not a blank node identifier.',
            'jsonld.SyntaxError', 'invalid type mapping',
            array('context' => $local_ctx));
        }
      }

      // add @type to mapping
      $mapping->{'@type'} = $type;
    }

    if(property_exists($value, '@container')) {
      $container = $value->{'@container'};
      if($container !== '@list' && $container !== '@set' &&
        $container !== '@index' && $container !== '@language') {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @container value must be ' .
          'one of the following: @list, @set, @index, or @language.',
          'jsonld.SyntaxError', 'invalid container mapping',
          array('context' => $local_ctx));
      }
      if($mapping->reverse && $container !== '@index' &&
        $container !== '@set' && $container !== null) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @container value for a @reverse ' +
          'type definition must be @index or @set.',
          'jsonld.SyntaxError', 'invalid reverse property',
          array('context' => $local_ctx));
      }

      // add @container to mapping
      $mapping->{'@container'} = $container;
    }

    if(property_exists($value, '@language') &&
      !property_exists($value, '@type')) {
      $language = $value->{'@language'};
      if($language !== null && !is_string($language)) {
        throw new JsonLdException(
          'Invalid JSON-LD syntax; @context @language value must be ' .
          'a string or null.', 'jsonld.SyntaxError',
          'invalid language mapping', array('context' => $local_ctx));
      }

      // add @language to mapping
      if($language !== null) {
        $language = strtolower($language);
      }
      $mapping->{'@language'} = $language;
    }

    // disallow aliasing @context and @preserve
    $id = $mapping->{'@id'};
    if($id === '@context' || $id === '@preserve') {
      throw new JsonLdException(
        'Invalid JSON-LD syntax; @context and @preserve cannot be aliased.',
        'jsonld.SyntaxError', 'invalid keyword alias',
        array('context' => $local_ctx));
    }
  }

  /**
   * Expands a string to a full IRI. The string may be a term, a prefix, a
   * relative IRI, or an absolute IRI. The associated absolute IRI will be
   * returned.
   *
   * @param stdClass $active_ctx the current active context.
   * @param string $value the string to expand.
   * @param assoc $relative_to options for how to resolve relative IRIs:
   *          base: true to resolve against the base IRI, false not to.
   *          vocab: true to concatenate after @vocab, false not to.
   * @param stdClass $local_ctx the local context being processed (only given
   *          if called during document processing).
   * @param defined a map for tracking cycles in context definitions (only given
   *          if called during document processing).
   *
   * @return mixed the expanded value.
   */
  function _expandIri(
    $active_ctx, $value, $relative_to=array(), $local_ctx=null, $defined=null) {
    // already expanded
    if($value === null || self::_isKeyword($value)) {
      return $value;
    }

    // define term dependency if not defined
    if($local_ctx !== null && property_exists($local_ctx, $value) &&
      !self::_hasKeyValue($defined, $value, true)) {
      $this->_createTermDefinition($active_ctx, $local_ctx, $value, $defined);
    }

    if(isset($relative_to['vocab']) && $relative_to['vocab']) {
      if(property_exists($active_ctx->mappings, $value)) {
        $mapping = $active_ctx->mappings->{$value};

        // value is explicitly ignored with a null mapping
        if($mapping === null) {
          return null;
        }

        // value is a term
        return $mapping->{'@id'};
      }
    }

    // split value into prefix:suffix
    $colon = strpos($value, ':');
    if($colon !== false) {
      $prefix = substr($value, 0, $colon);
      $suffix = substr($value, $colon + 1);

      // do not expand blank nodes (prefix of '_') or already-absolute
      // IRIs (suffix of '//')
      if($prefix === '_' || strpos($suffix, '//') === 0) {
        return $value;
      }

      // prefix dependency not defined, define it
      if($local_ctx !== null && property_exists($local_ctx, $prefix)) {
        $this->_createTermDefinition(
          $active_ctx, $local_ctx, $prefix, $defined);
      }

      // use mapping if prefix is defined
      if(property_exists($active_ctx->mappings, $prefix)) {
        $mapping = $active_ctx->mappings->{$prefix};
        if($mapping) {
          return $mapping->{'@id'} . $suffix;
        }
      }

      // already absolute IRI
      return $value;
    }

    // prepend vocab
    if(isset($relative_to['vocab']) && $relative_to['vocab'] &&
      property_exists($active_ctx, '@vocab')) {
      return $active_ctx->{'@vocab'} . $value;
    }

    // prepend base
    $rval = $value;
    if(isset($relative_to['base']) && $relative_to['base']) {
      $rval = jsonld_prepend_base($active_ctx->{'@base'}, $rval);
    }

    return $rval;
  }

  /**
   * Finds all @context URLs in the given JSON-LD input.
   *
   * @param mixed $input the JSON-LD input.
   * @param stdClass $urls a map of URLs (url => false/@contexts).
   * @param bool $replace true to replace the URLs in the given input with
   *           the @contexts from the urls map, false not to.
   * @param string $base the base URL to resolve relative URLs with.
   */
  protected function _findContextUrls($input, $urls, $replace, $base) {
    if(is_array($input)) {
      foreach($input as $e) {
        $this->_findContextUrls($e, $urls, $replace, $base);
      }
    } else if(is_object($input)) {
      foreach($input as $k => &$v) {
        if($k !== '@context') {
          $this->_findContextUrls($v, $urls, $replace, $base);
          continue;
        }

        // array @context
        if(is_array($v)) {
          $length = count($v);
          for($i = 0; $i < $length; ++$i) {
            if(is_string($v[$i])) {
              $url = jsonld_prepend_base($base, $v[$i]);
              // replace w/@context if requested
              if($replace) {
                $ctx = $urls->{$url};
                if(is_array($ctx)) {
                  // add flattened context
                  array_splice($v, $i, 1, $ctx);
                  $i += count($ctx) - 1;
                  $length = count($v);
                } else {
                  $v[$i] = $ctx;
                }
              } else if(!property_exists($urls, $url)) {
                // @context URL found
                $urls->{$url} = false;
              }
            }
          }
        } else if(is_string($v)) {
          // string @context
          $v = jsonld_prepend_base($base, $v);
          // replace w/@context if requested
          if($replace) {
            $input->{$k} = $urls->{$v};
          } else if(!property_exists($urls, $v)) {
            // @context URL found
            $urls->{$v} = false;
          }
        }
      }
    }
  }

  /**
   * Retrieves external @context URLs using the given document loader. Each
   * instance of @context in the input that refers to a URL will be replaced
   * with the JSON @context found at that URL.
   *
   * @param mixed $input the JSON-LD input with possible contexts.
   * @param stdClass $cycles an object for tracking context cycles.
   * @param callable $load_document(url) the document loader.
   * @param base $base the base URL to resolve relative URLs against.
   *
   * @return mixed the result.
   */
  protected function _retrieveContextUrls(
    &$input, $cycles, $load_document, $base='') {
    if(count(get_object_vars($cycles)) > self::MAX_CONTEXT_URLS) {
      throw new JsonLdException(
        'Maximum number of @context URLs exceeded.',
        'jsonld.ContextUrlError', 'loading remote context failed',
        array('max' => self::MAX_CONTEXT_URLS));
    }

    // for tracking the URLs to retrieve
    $urls = new stdClass();

    // regex for validating URLs
    $regex = '/(http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%@!\-\/]))?/';

    // find all URLs in the given input
    $this->_findContextUrls($input, $urls, false, $base);

    // queue all unretrieved URLs
    $queue = array();
    foreach($urls as $url => $ctx) {
      if($ctx === false) {
        // validate URL
        if(!preg_match($regex, $url)) {
          throw new JsonLdException(
            'Malformed or unsupported URL.', 'jsonld.InvalidUrl',
            'loading remote context failed', array('url' => $url));
        }
        $queue[] = $url;
      }
    }

    // retrieve URLs in queue
    foreach($queue as $url) {
      // check for context URL cycle
      if(property_exists($cycles, $url)) {
        throw new JsonLdException(
          'Cyclical @context URLs detected.',
          'jsonld.ContextUrlError', 'recursive context inclusion',
          array('url' => $url));
      }
      $_cycles = self::copy($cycles);
      $_cycles->{$url} = true;

      // retrieve URL
      $remote_doc = call_user_func($load_document, $url);
      $ctx = $remote_doc->document;

      // parse string context as JSON
      if(is_string($ctx)) {
        try {
          $ctx = self::_parse_json($ctx);
        } catch(Exception $e) {
          throw new JsonLdException(
            'Could not parse JSON from URL.',
            'jsonld.ParseError', 'loading remote context failed',
            array('url' => $url), $e);
        }
      }

      // ensure ctx is an object
      if(!is_object($ctx)) {
        throw new JsonLdException(
          'Derefencing a URL did not result in a valid JSON-LD object.',
          'jsonld.InvalidUrl', 'invalid remote context', array('url' => $url));
      }

      // use empty context if no @context key is present
      if(!property_exists($ctx, '@context')) {
        $ctx = (object)array('@context' => new stdClass());
      } else {
        $ctx = (object)array('@context' => $ctx->{'@context'});
      }

      // append context URL to context if given
      if($remote_doc->contextUrl !== null) {
        $ctx->{'@context'} = self::arrayify($ctx->{'@context'});
        $ctx->{'@context'}[] = $remote_doc->contextUrl;
      }

      // recurse
      $this->_retrieveContextUrls($ctx, $_cycles, $load_document, $url);
      $urls->{$url} = $ctx->{'@context'};
    }

    // replace all URLS in the input
    $this->_findContextUrls($input, $urls, true, $base);
  }

  /**
   * Gets the initial context.
   *
   * @param assoc $options the options to use.
   *          base the document base IRI.
   *
   * @return stdClass the initial context.
   */
  protected function _getInitialContext($options) {
    return (object)array(
      '@base' => jsonld_parse_url($options['base']),
      'mappings' => new stdClass(),
      'inverse' => null);
  }

  /**
   * Generates an inverse context for use in the compaction algorithm, if
   * not already generated for the given active context.
   *
   * @param stdClass $active_ctx the active context to use.
   *
   * @return stdClass the inverse context.
   */
  protected function _getInverseContext($active_ctx) {
    // inverse context already generated
    if($active_ctx->inverse) {
      return $active_ctx->inverse;
    }

    $inverse = $active_ctx->inverse = new stdClass();

    // variables for building fast CURIE map
    $fast_curie_map = $active_ctx->fast_curie_map = new ArrayObject();
    $iris_to_terms = array();

    // handle default language
    $default_language = '@none';
    if(property_exists($active_ctx, '@language')) {
      $default_language = $active_ctx->{'@language'};
    }

    // create term selections for each mapping in the context, ordered by
    // shortest and then lexicographically least
    $mappings = $active_ctx->mappings;
    $terms = array_keys((array)$mappings);
    usort($terms, array($this, '_compareShortestLeast'));
    foreach($terms as $term) {
      $mapping = $mappings->{$term};
      if($mapping === null) {
        continue;
      }

      // add term selection where it applies
      if(property_exists($mapping, '@container')) {
        $container = $mapping->{'@container'};
      } else {
        $container = '@none';
      }

      // iterate over every IRI in the mapping
      $iris = $mapping->{'@id'};
      $iris = self::arrayify($iris);
      foreach($iris as $iri) {
        $is_keyword = self::_isKeyword($iri);

        // initialize container map
        if(!property_exists($inverse, $iri)) {
          $inverse->{$iri} = new stdClass();
          if(!$is_keyword && !$mapping->_term_has_colon) {
            // init IRI to term map and fast CURIE map
            $iris_to_terms[$iri] = new ArrayObject();
            $iris_to_terms[$iri][] = $term;
            $fast_curie_entry = (object)array(
              'iri' => $iri, 'terms' => $iris_to_terms[$iri]);
            if(!array_key_exists($iri[0], (array)$fast_curie_map)) {
              $fast_curie_map[$iri[0]] = new ArrayObject();
            }
            $fast_curie_map[$iri[0]][] = $fast_curie_entry;
          }
        } else if(!$is_keyword && !$mapping->_term_has_colon) {
          // add IRI to term match
          $iris_to_terms[$iri][] = $term;
        }
        $container_map = $inverse->{$iri};

        // add new entry
        if(!property_exists($container_map, $container)) {
          $container_map->{$container} = (object)array(
            '@language' => new stdClass(),
            '@type' => new stdClass());
        }
        $entry = $container_map->{$container};

        if($mapping->reverse) {
          // term is preferred for values using @reverse
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@type'}, '@reverse');
        } else if(property_exists($mapping, '@type')) {
          // term is preferred for values using specific type
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@type'}, $mapping->{'@type'});
        } else if(property_exists($mapping, '@language')) {
          // term is preferred for values using specific language
          $language = $mapping->{'@language'};
          if($language === null) {
            $language = '@null';
          }
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@language'}, $language);
        } else {
          // term is preferred for values w/default language or no type and
          // no language
          // add an entry for the default language
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@language'}, $default_language);

          // add entries for no type and no language
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@type'}, '@none');
          $this->_addPreferredTerm(
            $mapping, $term, $entry->{'@language'}, '@none');
        }
      }
    }

    // build fast CURIE map
    foreach($fast_curie_map as $key => $value) {
      $this->_buildIriMap($fast_curie_map, $key, 1);
    }

    return $inverse;
  }

  /**
   * Runs a recursive algorithm to build a lookup map for quickly finding
   * potential CURIEs.
   *
   * @param ArrayObject $iri_map the map to build.
   * @param string $key the current key in the map to work on.
   * @param int $idx the index into the IRI to compare.
   */
  function _buildIriMap($iri_map, $key, $idx) {
    $entries = $iri_map[$key];
    $next = $iri_map[$key] = new ArrayObject();

    foreach($entries as $entry) {
      $iri = $entry->iri;
      if($idx >= strlen($iri)) {
        $letter = '';
      } else {
        $letter = $iri[$idx];
      }
      if(!isset($next[$letter])) {
        $next[$letter] = new ArrayObject();
      }
      $next[$letter][] = $entry;
    }

    foreach($next as $key => $value) {
      if($key === '') {
        continue;
      }
      $this->_buildIriMap($next, $key, $idx + 1);
    }
  }

  /**
   * Adds the term for the given entry if not already added.
   *
   * @param stdClass $mapping the term mapping.
   * @param string $term the term to add.
   * @param stdClass $entry the inverse context type_or_language entry to
   *          add to.
   * @param string $type_or_language_value the key in the entry to add to.
   */
  function _addPreferredTerm($mapping, $term, $entry, $type_or_language_value) {
    if(!property_exists($entry, $type_or_language_value)) {
      $entry->{$type_or_language_value} = $term;
    }
  }

  /**
   * Clones an active context, creating a child active context.
   *
   * @return stdClass a clone (child) of the active context.
   */
  protected function _cloneActiveContext($active_ctx) {
    $child = new stdClass();
    $child->{'@base'} = $active_ctx->{'@base'};
    $child->mappings = self::copy($active_ctx->mappings);
    $child->inverse = null;
    if(property_exists($active_ctx, '@language')) {
      $child->{'@language'} = $active_ctx->{'@language'};
    }
    if(property_exists($active_ctx, '@vocab')) {
      $child->{'@vocab'} = $active_ctx->{'@vocab'};
    }
    return $child;
  }

  /**
   * Returns whether or not the given value is a keyword.
   *
   * @param string $v the value to check.
   *
   * @return bool true if the value is a keyword, false if not.
   */
  protected static function _isKeyword($v) {
    if(!is_string($v)) {
      return false;
    }
    switch($v) {
    case '@base':
    case '@context':
    case '@container':
    case '@default':
    case '@embed':
    case '@explicit':
    case '@graph':
    case '@id':
    case '@index':
    case '@language':
    case '@list':
    case '@omitDefault':
    case '@preserve':
    case '@requireAll':
    case '@reverse':
    case '@set':
    case '@type':
    case '@value':
    case '@vocab':
      return true;
    }
    return false;
  }

  /**
   * Returns true if the given value is an empty Object.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is an empty Object, false if not.
   */
  protected static function _isEmptyObject($v) {
    return is_object($v) && count(get_object_vars($v)) === 0;
  }

  /**
   * Throws an exception if the given value is not a valid @type value.
   *
   * @param mixed $v the value to check.
   */
  protected static function _validateTypeValue($v) {
    // must be a string or empty object
    if(is_string($v) || self::_isEmptyObject($v)) {
      return;
    }

    // must be an array
    $is_valid = false;
    if(is_array($v)) {
      // must contain only strings
      $is_valid = true;
      foreach($v as $e) {
        if(!(is_string($e))) {
          $is_valid = false;
          break;
        }
      }
    }

    if(!$is_valid) {
      throw new JsonLdException(
        'Invalid JSON-LD syntax; "@type" value must a string, an array ' .
        'of strings, or an empty object.',
        'jsonld.SyntaxError', 'invalid type value', array('value' => $v));
    }
  }

  /**
   * Returns true if the given value is a subject with properties.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is a subject with properties, false if not.
   */
  protected static function _isSubject($v) {
    // Note: A value is a subject if all of these hold true:
    // 1. It is an Object.
    // 2. It is not a @value, @set, or @list.
    // 3. It has more than 1 key OR any existing key is not @id.
    $rval = false;
    if(is_object($v) &&
      !property_exists($v, '@value') &&
      !property_exists($v, '@set') &&
      !property_exists($v, '@list')) {
      $count = count(get_object_vars($v));
      $rval = ($count > 1 || !property_exists($v, '@id'));
    }
    return $rval;
  }

  /**
   * Returns true if the given value is a subject reference.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is a subject reference, false if not.
   */
  protected static function _isSubjectReference($v) {
    // Note: A value is a subject reference if all of these hold true:
    // 1. It is an Object.
    // 2. It has a single key: @id.
    return (is_object($v) && count(get_object_vars($v)) === 1 &&
      property_exists($v, '@id'));
  }

  /**
   * Returns true if the given value is a @value.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is a @value, false if not.
   */
  protected static function _isValue($v) {
    // Note: A value is a @value if all of these hold true:
    // 1. It is an Object.
    // 2. It has the @value property.
    return is_object($v) && property_exists($v, '@value');
  }

  /**
   * Returns true if the given value is a @list.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is a @list, false if not.
   */
  protected static function _isList($v) {
    // Note: A value is a @list if all of these hold true:
    // 1. It is an Object.
    // 2. It has the @list property.
    return is_object($v) && property_exists($v, '@list');
  }

  /**
   * Returns true if the given value is a blank node.
   *
   * @param mixed $v the value to check.
   *
   * @return bool true if the value is a blank node, false if not.
   */
  protected static function _isBlankNode($v) {
    // Note: A value is a blank node if all of these hold true:
    // 1. It is an Object.
    // 2. If it has an @id key its value begins with '_:'.
    // 3. It has no keys OR is not a @value, @set, or @list.
    $rval = false;
    if(is_object($v)) {
      if(property_exists($v, '@id')) {
        $rval = (strpos($v->{'@id'}, '_:') === 0);
      } else {
        $rval = (count(get_object_vars($v)) === 0 ||
          !(property_exists($v, '@value') ||
            property_exists($v, '@set') ||
            property_exists($v, '@list')));
      }
    }
    return $rval;
  }

  /**
   * Returns true if the given value is an absolute IRI, false if not.
   *
   * @param string $v the value to check.
   *
   * @return bool true if the value is an absolute IRI, false if not.
   */
  protected static function _isAbsoluteIri($v) {
    return strpos($v, ':') !== false;
  }

  /**
   * Returns true if the given target has the given key and its
   * value equals is the given value.
   *
   * @param stdClass $target the target object.
   * @param string key the key to check.
   * @param mixed $value the value to check.
   *
   * @return bool true if the target has the given key and its value matches.
   */
  protected static function _hasKeyValue($target, $key, $value) {
    return (property_exists($target, $key) && $target->{$key} === $value);
  }

  /**
   * Returns true if both of the given objects have the same value for the
   * given key or if neither of the objects contain the given key.
   *
   * @param stdClass $o1 the first object.
   * @param stdClass $o2 the second object.
   * @param string key the key to check.
   *
   * @return bool true if both objects have the same value for the key or
   *   neither has the key.
   */
  protected static function _compareKeyValues($o1, $o2, $key) {
    if(property_exists($o1, $key)) {
      return property_exists($o2, $key) && $o1->{$key} === $o2->{$key};
    }
    return !property_exists($o2, $key);
  }

  /**
   * Parses JSON and sets an appropriate exception message on error.
   *
   * @param string $json the JSON to parse.
   *
   * @return mixed the parsed JSON object or array.
   */
  protected static function _parse_json($json) {
    $rval = json_decode($json);
    $error = json_last_error();
    if($error === JSON_ERROR_NONE && $rval === null) {
      $error = JSON_ERROR_SYNTAX;
    }
    switch($error) {
    case JSON_ERROR_NONE:
      break;
    case JSON_ERROR_DEPTH:
      throw new JsonLdException(
        'Could not parse JSON; the maximum stack depth has been exceeded.',
        'jsonld.ParseError');
    case JSON_ERROR_STATE_MISMATCH:
      throw new JsonLdException(
        'Could not parse JSON; invalid or malformed JSON.',
        'jsonld.ParseError');
    case JSON_ERROR_CTRL_CHAR:
    case JSON_ERROR_SYNTAX:
      throw new JsonLdException(
        'Could not parse JSON; syntax error, malformed JSON.',
        'jsonld.ParseError');
    case JSON_ERROR_UTF8:
      throw new JsonLdException(
        'Could not parse JSON from URL; malformed UTF-8 characters.',
        'jsonld.ParseError');
    default:
      throw new JsonLdException(
        'Could not parse JSON from URL; unknown error.',
        'jsonld.ParseError');
    }
    return $rval;
  }
}

// register the N-Quads RDF parser
jsonld_register_rdf_parser(
  'application/nquads', array('JsonLdProcessor', 'parseNQuads'));

/**
 * A JSON-LD Exception.
 */
class JsonLdException extends Exception {

  protected $type;
  protected $code;
  protected $details;
  protected $cause;

  public function __construct(
    $msg, $type, $code='error', $details=null, $previous=null) {
    $this->type = $type;
    $this->code = $code;
    $this->details = $details;
    $this->cause = $previous;
    parent::__construct($msg, 0, $previous);
  }
  public function __toString() {
    $rval = __CLASS__ . ": [{$this->type}]: {$this->message}\n";
    if($this->code) {
      $rval .= 'Code: ' . $this->code . "\n";
    }
    if($this->details) {
      $rval .= 'Details: ' . print_r($this->details, true) . "\n";
    }
    if($this->cause) {
      $rval .= 'Cause: ' . $this->cause;
    }
    $rval .= $this->getTraceAsString() . "\n";
    return $rval;
  }
};

/**
 * A UniqueNamer issues unique names, keeping track of any previously issued
 * names.
 */
class UniqueNamer {
  /**
   * Constructs a new UniqueNamer.
   *
   * @param prefix the prefix to use ('<prefix><counter>').
   */

  public $prefix;
  public $counter;
  public $existing;
  public $order;

  public function __construct($prefix) {
    $this->prefix = $prefix;
    $this->counter = 0;
    $this->existing = new stdClass();
    $this->order = array();
  }

  /**
   * Clones this UniqueNamer.
   */
  public function __clone() {
    $this->existing = clone $this->existing;
  }

  /**
   * Gets the new name for the given old name, where if no old name is given
   * a new name will be generated.
   *
   * @param mixed [$old_name] the old name to get the new name for.
   *
   * @return string the new name.
   */
  public function getName($old_name=null) {
    // return existing old name
    if($old_name && property_exists($this->existing, $old_name)) {
      return $this->existing->{$old_name};
    }

    // get next name
    $name = $this->prefix . $this->counter;
    $this->counter += 1;

    // save mapping
    if($old_name !== null) {
      $this->existing->{$old_name} = $name;
      $this->order[] = $old_name;
    }

    return $name;
  }

  /**
   * Returns true if the given old name has already been assigned a new name.
   *
   * @param string $old_name the old name to check.
   *
   * @return true if the old name has been assigned a new name, false if not.
   */
  public function isNamed($old_name) {
    return property_exists($this->existing, $old_name);
  }
}

/**
 * A Permutator iterates over all possible permutations of the given array
 * of elements.
 */
class Permutator {
  /**
   * Constructs a new Permutator.
   *
   * @param array $list the array of elements to iterate over.
   */

  public $list;
  public $done;
  public $left;

  public function __construct($list) {
    // original array
    $this->list = $list;
    sort($this->list);
    // indicates whether there are more permutations
    $this->done = false;
    // directional info for permutation algorithm
    $this->left = new stdClass();
    foreach($list as $v) {
      $this->left->{$v} = true;
    }
  }

  /**
   * Returns true if there is another permutation.
   *
   * @return bool true if there is another permutation, false if not.
   */
  public function hasNext() {
    return !$this->done;
  }

  /**
   * Gets the next permutation. Call hasNext() to ensure there is another one
   * first.
   *
   * @return array the next permutation.
   */
  public function next() {
    // copy current permutation
    $rval = $this->list;

    /* Calculate the next permutation using the Steinhaus-Johnson-Trotter
     permutation algorithm. */

    // get largest mobile element k
    // (mobile: element is greater than the one it is looking at)
    $k = null;
    $pos = 0;
    $length = count($this->list);
    for($i = 0; $i < $length; ++$i) {
      $element = $this->list[$i];
      $left = $this->left->{$element};
      if(($k === null || $element > $k) &&
        (($left && $i > 0 && $element > $this->list[$i - 1]) ||
        (!$left && $i < ($length - 1) && $element > $this->list[$i + 1]))) {
        $k = $element;
        $pos = $i;
      }
    }

    // no more permutations
    if($k === null) {
      $this->done = true;
    } else {
      // swap k and the element it is looking at
      $swap = $this->left->{$k} ? $pos - 1 : $pos + 1;
      $this->list[$pos] = $this->list[$swap];
      $this->list[$swap] = $k;

      // reverse the direction of all elements larger than k
      for($i = 0; $i < $length; ++$i) {
        if($this->list[$i] > $k) {
          $this->left->{$this->list[$i]} = !$this->left->{$this->list[$i]};
        }
      }
    }

    return $rval;
  }
}

/**
 * An ActiveContextCache caches active contexts so they can be reused without
 * the overhead of recomputing them.
 */
class ActiveContextCache {
  /**
   * Constructs a new ActiveContextCache.
   *
   * @param int size the maximum size of the cache, defaults to 100.
   */

  private $order;
  private $cache;
  private $size;

  public function __construct($size=100) {
    $this->order = array();
    $this->cache = new stdClass();
    $this->size = $size;
  }

  /**
   * Gets an active context from the cache based on the current active
   * context and the new local context.
   *
   * @param stdClass $active_ctx the current active context.
   * @param stdClass $local_ctx the new local context.
   *
   * @return mixed a shared copy of the cached active context or null.
   */
  public function get($active_ctx, $local_ctx) {
    $key1 = serialize($active_ctx);
    $key2 = serialize($local_ctx);
    if(property_exists($this->cache, $key1)) {
      $level1 = $this->cache->{$key1};
      if(property_exists($level1, $key2)) {
        return $level1->{$key2};
      }
    }
    return null;
  }

  /**
   * Sets an active context in the cache based on the previous active
   * context and the just-processed local context.
   *
   * @param stdClass $active_ctx the previous active context.
   * @param stdClass $local_ctx the just-processed local context.
   * @param stdClass $result the resulting active context.
   */
  public function set($active_ctx, $local_ctx, $result) {
    if(count($this->order) === $this->size) {
      $entry = array_shift($this->order);
      unset($this->cache->{$entry->activeCtx}->{$entry->localCtx});
    }
    $key1 = serialize($active_ctx);
    $key2 = serialize($local_ctx);
    $this->order[] = (object)array(
      'activeCtx' => $key1, 'localCtx' => $key2);
    if(!property_exists($this->cache, $key1)) {
      $this->cache->{$key1} = new stdClass();
    }
    $this->cache->{$key1}->{$key2} = JsonLdProcessor::copy($result);
  }
}

/* end of file, omit ?> */