forked from vanthome/rest-api-essay-presentation
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathrest_apis.html
1056 lines (710 loc) · 25.6 KB
/
rest_apis.html
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
452
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
<!DOCTYPE html>
<html>
<head>
<title>REST APIs Today and Tomorrow -- an essay</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<style type="text/css">
@import url(//fonts.googleapis.com/css?family=Yanone+Kaffeesatz);
@import url(//fonts.googleapis.com/css?family=Droid+Serif:400,700,400italic);
@import url(//fonts.googleapis.com/css?family=Ubuntu+Mono:400,700,400italic);
body { font-family: 'Droid Serif'; }
h1, h2, h3 {
font-family: 'Yanone Kaffeesatz';
font-weight: normal;
}
.remark-code, .remark-inline-code { font-family: 'Ubuntu Mono'; }
.red { color: red; }
blockquote { background-color: lightgray; font-family: serif; }
img { max-width: 100%; }
small { font-size: 70%; }
iframe { width: 100%; height: 25em; }
table { border-collapse: collapse; }
table td { border: 1px solid black; padding: 0.2em; }
/* Two-column layout */
.left-column {
width: 48%;
height: 92%;
float: left;
}
.right-column {
width: 48%;
float: right;
}
</style>
</head>
<body>
<textarea id="source">
class: center, middle
# REST APIs Today and Tomorrow
## an Essay
Thomas Hoppe in 2015
---
# Contents
1. Relevance of Web APIs
2. History of distributed System Integration Paradigms
3. What actually is REST?
4. The Semantic Web
5. Linked Data
6. JSON-LD
7. Hydra Core
---
class: center, middle
# Relevance of Web APIs
---
# Relevance of Web APIs
**API First!**
<br>
<small>
It's no longer Web first or mobile first.
</small>
<br><br>
**We live in an _API Economy_.** [1][1]
<br><br>
**The _Chief API Officer_ term is coined.** [2][2]
<br><br>
**If it's not programmable, it doesn't exist.**
<br>
<small>
by me :)
</small>
[1]: http://www.forbes.com/sites/ciocentral/2012/08/29/welcome-to-the-api-economy/
[2]: http://www.citeworld.com/article/2115558/development/chief-api-officer.html
---
class: center, middle
# History of distributed System Integration Paradigms
---
# Non-scientific enumeration of past Hypes
- Integrated via asynchronous messaging (MQ).
- Popular when mainframes were hip.
- Remote Procedure Calls (RPC).
- Often with CORBA as a protocol.
- Service Oriented Architecture (SOA).
- Still popular in enterprise IT but irrelevant for mobile computing.
- Although not mandated, the integration protocol of choice in SOAs is/ was SOAP/HTTP and SOAP via asynchronous protocols.
- Pseudo-REST APIs ‒ <span class="red">today<span>.
- "pseudo" because they do not fulfill all of the commonly accepted criteria of a REST API.
---
# Prospected Future
- REST APIs ‒ **approaching**.
- Semantic REST APIs ‒ **future**.
Both are further elaborated below.
---
# SOA vs. REST (1/2)
Google trends for the terms _SOAP API_ and _REST API_:
<iframe src="//www.google.com/trends/fetchComponent?hl=en-US&q=soap+api,+rest+api&cmpt=q&content=1&cid=TIMESERIES_GRAPH_0&export=5&w=650&h=330" style="border: none;" height="330" width="650"></iframe>
<small>Generally a weak comparision, yes, but is significant for our purpose.</small>
---
# SOA vs. REST (2/2)
In one of the largest independent and publicly available directories for APIs, the Programmableweb,
the share of Internet APIs by technology in March 2014 is:
REST (69%), SOAP (18%), JavaScript (5%), and XML-RPC (2%).
<!--
# REST is still on the Rise
http://de.slideshare.net/programmableweb/web-api-growthsince2005
-->
---
# Qualitative Advantages of REST over SOAP
- Developers like REST because the learning curve is less steep.
- Web Services' contract first appraoch (early binding) is more complex.
- It requires a longer/ deeper toolchain to be equally productive.
- Better client support in most languages.
- SOAP clients for PHP and NodeJS are still not on par with Java.
- The whole footprint of SOAP is too big for mobile.
- Parsing of JSON is less compute and memory intensive than XML.
- Required technology stack is more complex.
---
# Conclusions
1. We saw an exponential growth of the number of offered WEB APIs.
2. In the future of distributed systems computing, most likely only REST and SOA will be relevant
for distributed system integration.
3. SOAP will persist for specialized enterprise
interfaces as part of SOAs and in B2B scenarios.
---
class: center, middle
# What actually is REST?
---
# The Beginning
- **2000:** The doctoral dissertation from Roy Fielding is commonly reckoned as the manifesto of the REST API vision.
<iframe src="http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm"></iframe>
---
# A Definition
### <span class="red">Re</span>presentational <span class="red">S</span>tate <span class="red">T</span>ransfer.
> REST is an architectural style consisting of a coordinated set of architectural constraints applied to components,
connectors, and data elements, within a distributed hypermedia system.
<br><small>‒ http://en.wikipedia.org/wiki/Representational_state_transfer</small>
<br>
“Representation”: A way of formatting/ serializing a resource, such as JSON, HTML, PNG.
---
# What REST isn't / what you can't do with it
- It's not a product → you cannot buy it.
- It is not a (Web) standard.
- It's not a protocol or about a single protocol (HTTP).
- There is no reference implementation.
---
# The Past Drivers
- **2006:** API pioneers eBay, Amazon and Google Maps were among the first to offer popular Web APIs.
- **2007:** The mobile revolution kicked of by smart phones.
- **2013:** Mobile and infotainment platforms diversity (Jolla, BB10, Tizen, Ubuntu, WP, FF OS, Android...).
# Future Drivers
- **2015+:** Babylonic language diversity (Only some newer ones: Rust, Go, Dart).
<!--
developers like SDKs but is it realistic for an API provider to offer an SDK for `n` languages?
-->
- **2016+:** Internet of things (vehicles, household appliances, ...every power plug).
- 15B connected devices in 2015, 40B connected devices in 2020.
---
# REST Constraints (1/2)
The essence of Fieldings thesis is the following series of constraints:
- Client-server.
<small>
_separation of concerns_ — A clean separation of duty exists between client and server;
server is responsible for data processing and persistence, client to drive the interaction.
</small>
- Stateless.
<small>
Server must only use the data in a request to service it; no further context info.
</small>
- Cacheable.
<small>
The data within a response to a request must be implicitly or explicitly labeled as cacheable or non-cacheable.
</small>
- Layered system.
<small>
Servers do not know whether there are layers of abstraction between themselves and the end client.
</small>
<!--
http://kellabyte.com/2011/09/04/clarifying-rest/
http://en.wikipedia.org/wiki/Representational_state_transfer
http://www.pwc.com/us/en/technology-forecast/2012/issue2/features/feature-consumerization-apis.jhtml
-->
---
# REST Constraints (2/2)
- Code on demand (optional).
<small>
Servers can temporarily extend or customize the functionality of a client by the transfer of executable code.
</small>
- Uniform interface:
- Identification of resources (not a representation).
<small>
Individual resources are identifiable with a GUID.
</small>
- Manipulation via representations.
<small>
Possible interactions can be introspected.
</small>
- Self descriptive messages.
<small>
A resource can be understood syntactucally and semantically from the carried data and meta-data.
</small>
- Hypermedia as the engine of application state (HATEOAS).
<small>
Clients make state transitions only through actions that are dynamically identified within hypermedia by the server.
</small>
---
# The Hypermedia Constraint (1/2)
- is often-overlooked; ~99% of existing APIs don't do this right,
- is not particularly easy to achieve as it requires quite some effort (and a smart client),
- is the main enabler for the _loose coupling_ principle.
---
# The Hypermedia Constraint (2/2)
Consider that an API client can be modelled as a state machine.
The hypermedia constraint says that the client must be able to use the API
without knowing this state machine at design time.
Consequence: Resources must describe their
- Relations,
- Affordances (possible operations).
---
# Client State Machine Example
<img style="max-width: 80%;" src="https://docs.google.com/drawings/d/1qjYy-MAiUOslhLPDZLuJCjjukyyyVdPWSxevPsjOuhY/pub?w=960&h=720" alt="Client App State Machine">
<small>http://www.programmableweb.com/news/hypermedia-apis-benefits-hateoas/how-to/2014/02/27</small>
<!--
See also:
https://www.arangodb.com/2014/12/02/building-hypermedia-apis-design
-->
---
# But what is all this good for?
Put in some quotes:
<br>
> A REST API is just a Web site for users with a limited vocabulary.
<br><small>‒ Roy Fielding in 2013</small>
<br>
<br>
> You are the most advanced API client while using your browser.
We need to enable machines acting on your behalf to acomplish
the same tasks through future APIs.
<br><small>‒ Thomas Hoppe, 2015</small>
<br>
<br>
---
# What we gain from real REST
Put in hard facts:
- URLs can change without breaking clients,
- Resource representations can change in terms of:
- Granularity,
- Affordances,
- Relations.
__→ Client and Server can evolve independently.__
- Discoverability,
- Performance through cacheability.
---
# The ultimate Test
Provide an API client with just the __entry point__ of your API.
If this is sufficient for the client to use the API in its entirety,
the API adheres to at least a good subset of the REST constraints.
And the client is a proper REST client.
---
# What do pseudo REST APIs wrong?
In the case of HTTP based REST:
- Interact only with a single endpoint instead of resources.
- Use HTTP as tunneling protocol.
- RPCish interaction (command messages) interaction.
- No hypermedia, no HATEOAS.
- Assumptions about available representations and transitions are hard-coded (or configured).
- Stateful communication.
- Resources/ messages/ data is not self-descriptive.
- Appropriate HTTP methods are not used; e. g. only GET.
- Content negotiation is not used.
- Proper HTTP response codes are not provided/ interpreted.
<!--
See RMM
http://martinfowler.com/articles/richardsonMaturityModel.html
-->
---
# Versioning
> Versioning an interface is just a polite way to kill deployed applications
<br><small>‒ Roy Fielding in 2013</small>
When did you last see a version on a Web site?
---
# Notable Qualities about HTTP Methods
Read only:
- GET,
- HEAD,
- OPTIONS.
Idempotent:
- PUT,
- DELETE.
Potentially idempotent:
- POST.
---
# So aren't there existing approaches?
Sure, here are a few media types which are at least hypermedia-aware:
- HAL <small>http://stateless.co/hal_specification.html</small>.
- SIREN <small>https://github.com/kevinswiber/siren</small>.
- SVG, Atom, (X)HTML(!).
- JSON Hyper-Schema <small>http://json-schema.org/</small>.
- JSON API <small>http://jsonapi.org/</small>.
- UBER Hypermedia <small>http://uberhypermedia.org/</small>.
<small>Note: JSON itself is not hypermedia-aware.</small>
My conclusion about them is, however, that most of them only address
the hypermedia issue but all of them lack at least one of the following features:
- Describing complex affordances like contextual actions/ operations.
- Provide a possbility to represent data really in a self-descripive manner.
→ Let's see whether we can do better.
---
class: center, middle
# The Semantic Web
---
# Ehrrm, isn't this long time dead?!
In the form which has been procalimed for decades ‒ probably yes.
---
# The Semantic Web technology Stack
---
# So what were the Issues?
- Complexity (full stack including ontologies).
- No comprehensible value add.
- Triplestores:
- immature,
- slow,
- only few implementations (very few commercial).
- SPARQL:
- complex,
- few implementations,
- inappropriate for many real-world problems.
- No killer application.
- For a long time it was a rather academic topic.
---
# RDF
<span class="red">R</span>esource <span class="red">D</span>escription <span class="red">F</span>ramework.
- Effectively a data model for labeled, directed multi-graphs.
- There is a variety of serialization formats
(e. g. RDF/XML, N3, Turtle, N-Triples, JSON-LD).
- Consists of statements about “things” (Web resources)
in the form of subject-predicate-object expressions, also known as triples.
- Statements can describe facts with literals,
- and interrelations to other things.
<!--
http://www.uni-weimar.de/medien/webis/teaching/lecturenotes/web-technology/unit-de-semantic-web-rdfs.pdf
-->
---
# RDF Examples
<small>
With literals / or in natural language:
| Subject | Predicate | Object |
|-------------------|------------------|------------------------------------|
| Thomas Hoppe | is interested in | REST |
With identifiable resources/ relations:
| Subject | Predicate | Object |
|-------------------|------------------|------------------------------------|
| th: | foaf:interest | wp:Representational_state_transfer |
With multiple statements:
| Subject | Predicate | Object |
|-------------------|------------------------|------------------------------------|
| th: | foaf:interest | wp:Representational_state_transfer |
| th: | foaf:firstName | Thomas |
| th: | foaf:lastName | Hoppe |
| th: | foaf:workplaceHomepage | http://www.n-fuse.de |
</small>
Prefixes:
<small>
foaf: http://xmlns.com/foaf/0.1/<br>
th: http://thomashoppe.me<br>
wp: http://en.wikipedia.org/wiki/<br>
</small>
---
# Some Definitions
“Resource”: A uniquely identifiable thing, typically identified by an IRI.
“Subject”: The resource a statement is about.
“Predicate”: A term used to describe or modify some aspect of the subject.
Usually it denotes relationships between the subject and the object.
“Object”: In English the object of a sentence is the thing that the verb is
acting upon. In RDF, it’s the “target” or “value” of the triple.
“Literal”: Can be untyped i. e. just a string or can be typed.
The types are again just RDF resources. It is, however, recommeded to use
XSD types such as `http://www.w3.org/2001/XMLSchema#int` whenever possible.
Untyped literals can in addition have an optional language tag.
<!--
information resource - A resource for which all essential characteristics can be transmitted in a message (i.e. a digital resource). Historically, information resources have been the primary focus of the Web. When most users enter a URL into a web browser, they assume that the result will be the return of an information resource in the form of a digital file. Examples: html web page, digital image, pfd file.
non-information resource - A resource that cannot be transmitted electronically. Non-information resources can be further subdivided into the following categories:
- physical resource - a material thing. Examples: an animal, a specimen, a 35 mm slide
- abstract resource - a non-material, non-electronic thing. Examples: a taxonomic concept, a relationship, a determination
-->
---
# Potential Values of Triple Elements
__Subject__: Only resources.
__Predicate__: Only resources.
__Object__: Resource or literals.
---
# Vocabularies
__Goal__: Establish common, shared terms for a domain.
__Comprising__:
- Individuals (instances, objects),
- Classes (concepts, types),
- Properties (relations, roles),
- Rules (axioms)
There are multiple vocabularies, to define vocabularies such as RDFS and OWL.
If they are rather complex (meany), they are also called _ontologies_.
Technically they are nothing else than a bunch of RDF resources which
are mostly used as predicates in other RDF resources.
<!--
http://www.w3.org/standards/semanticweb/ontology
-->
---
# Some Established Vocabularies
.left-column[
<small>
- rdf http://www.w3.org/1999/02/22-rdf-syntax-ns#
- rdfs http://www.w3.org/2000/01/rdf-schema#
- xsd http://www.w3.org/2001/XMLSchema#
- owl http://www.w3.org/2002/07/owl#
- skos http://www.w3.org/2004/02/skos/core#
- dir http://dir.w3.org/directory/schema#
- org http://www.w3.org/ns/org#
- rov http://www.w3.org/ns/regorg#
- dct http://purl.org/dc/terms/
- http http://www.w3.org/2011/http#
- httph http://www.w3.org/2011/http-headers#
- hydra http://www.w3.org/ns/hydra/core#
- cc http://creativecommons.org/ns#
- foaf http://xmlns.com/foaf/0.1/
- sioc http://rdfs.org/sioc/ns#
- geo http://www.w3.org/2003/01/geo/wgs84_pos#
- gn http://www.geonames.org/ontology#
</small>
]
.right-column[
<small>
- og http://ogp.me/ns#
- gr http://purl.org/goodrelations/v1#
- xro http://purl.org/xro/ns#
- dbo http://dbpedia.org/ontology/
- schema http://schema.org/
- tzont http://www.w3.org/2006/timezone#
- lingvo http://www.lingvoj.org/ontology#
- lvont http://lexvo.org/ontology#
- vs http://www.w3.org/2003/06/sw-vocab-status/ns#
- pto http://www.productontology.org/id/
- vann http://purl.org/vocab/vann/
- prov http://www.w3.org/ns/prov#
- doap http://usefulinc.com/ns/doap#
- voaf http://purl.org/vocommons/voaf#
- void http://rdfs.org/ns/void#
- adms http://www.w3.org/ns/adms#
</small>
]
---
class: center, middle
# Linked Data
---
# Linked Data
- It's about things and their relations, not about documents.
- For me something like the second take on the Semantic Web.
- Still based on RDF and co.
- Ultimate objective: Make the Web a single database.
<small>
More:
- https://www.youtube.com/watch?v=4x_xzT5eF5Q
</small>
---
# Linked Data Objective (1/2)
To get from a Web of documents...
<small>http://www.bbc.co.uk/staticarchive/533355da9de4faf21572098cf6aafa5a97795bce.png</small>
<!--
- Degree of structure in data: fairly low
- Designed for: human consumption
-->
---
# Linked Data Objective (2/2)
...to a Web of data (facts and relations).
<small>http://www.bbc.co.uk/staticarchive/392887acaaad47e534390f2c7d3910f2bf380a2e.png</small>
<!--
- Primary objects: “things” (or description of things)
- Links between “things”
- Degree of Structure: High (based on RDF data model)
- Explicit semantics of contents and links
- Designed for: Both machines and humans
-->
---
# Linked Data Principes
1. Use **URIs to denote things**.
2. Use **HTTP URIs** so that these things can be referred to and **looked up** ("dereferenced") by people and user agents.
3. **Provide useful information about the thing when its URI is dereferenced**, leveraging standards such as RDF, SPARQL.
4. Include **links to other related things** (using their URIs) when publishing data on the Web.
<small>Tim Berners-Lee, 2006<small>
---
# URLs, URIs, IRIs WTF?
- In the past, the Semantic Web was all about URIs.
- In 2005 they made they gained Unicode support with IRIs.
- URLs are just URIs/ IRIs which can be dereferenced.
---
# Linked Data Components
- URIs (specifically, of the dereferenceable variety).
- HTTP.
- Resource Description Framework (RDF).
- Serialization formats (RDFa, RDF/XML, N3, Turtle, JSON-LD, and others).
---
class: center, middle
# JSON-LD
---
# JSON-LD
<span class="red">JSON</span> <span class="red">L</span>inked <span class="red">D</span>ata; a serialization format for RDF.
> The desire for __better Web APIs__ is what motivated the creation of JSON-LD, not the Semantic Web.
If you want to make the Semantic Web a reality, stop making the case for it and spend your
time doing something more useful, like actually making machines smarter
or helping people publish data in a way that’s useful to them.
<br><small>‒ Manu Sporny [JSON-LD and why I hate the Semantic Web](http://manu.sporny.org/2014/json-ld-origins-2/)</small>
---
# Currently in _Recommendation_ state
<iframe src="http://www.w3.org/TR/json-ld/"></iframe>
---
# JSON-LD by Example (1/2)
Plain JSON:
````
{
"id": "http://thomashoppe.me",
"firstName": "Thomas",
"lastName": "Hoppe",
"workplaceHomepage": "http://www.n-fuse.de"
}
````
JSON-LD:
````
{
"@id": "http://thomashoppe.me",
"http://xmlns.com/foaf/0.1/firstName": "Thomas",
"http://xmlns.com/foaf/0.1/lastName": "Hoppe",
"http://xmlns.com/foaf/0.1/workplaceHomepage": "http://www.n-fuse.de"
}
````
---
# JSON-LD by Example (2/2)
Using an `@context` to shorten things and typing it using `@type`:
````
{
"@context": {
"id": "@id",
"foaf": "http://xmlns.com/foaf/0.1/",
"firstName": "foaf:firstName",
"lastName": "foaf:lastName",
"workplaceHomepage": "foaf:workplaceHomepage"
},
"@type": "foaf:Person",
"id": "http://thomashoppe.me",
"firstName": "Thomas",
"lastName": "Hoppe",
"workplaceHomepage": "http://www.n-fuse.de"
}
````
The `@context` can also be announced with an appropriate header:
<small>
`Link: <http://thomashoppe.me/person.jsonld>; rel="http://www.w3.org/ns/json-ld#context"; type="application/ld+json"`
</small>
---
# Polymorphy of JSON-LD and Compaction
JSON documents __1__ & __2__ are semantically equivalent:
__1:__
````
{
"@id": "http://thomashoppe.me",
"http://xmlns.com/foaf/0.1/firstName": "Thomas"
}
````
__2:__
````
{
"@context": {
"id": "@id",
"foaf": "http://xmlns.com/foaf/0.1/",
"firstName": "foaf:firstName"
},
"id": "http://thomashoppe.me",
"firstName": "Thomas"
}
````
I can transform 1 into 2 with the `@context` of 2 and the JSON-LD
__compaction__. See
[playground example](http://json-ld.org/playground/index.html#startTab=tab-compacted&json-ld=%7B%22%40id%22%3A%22http%3A%2F%2Fthomashoppe.me%22%2C%22http%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2FfirstName%22%3A%22Thomas%22%7D&context=%7B%22id%22%3A%22%40id%22%2C%22foaf%22%3A%22http%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%22%2C%22firstName%22%3A%22foaf%3AfirstName%22%7D).
---
# Declaring Links in JSON-LD
````
{
"@context": {
...
"workplaceHomepage": {
"@type": "@id",
"@id": "foaf:workplaceHomepage"
}
},
...
"workplaceHomepage": "http://www.n-fuse.de"
}
````
<br>
Effectively, this declares that the value of the `workplaceHomepage` property
is a resource.
<!--
The effect in N-Quads:
````
_:b0 <foaf:workplaceHomepage> <http://www.n-fuse.de> .
vs. without @id
_:b0 <foaf:workplaceHomepage> "http://www.n-fuse.de" .
````
-->
---
# More about JSON-LD
- https://www.youtube.com/watch?v=vioCbTo3C-4
- http://de.slideshare.net/lanthaler/building-next-generation-web-ap-is-with-jsonld-and-hydra?next_slideshow=1
- http://json-ld.org/playground/
---
class: center, middle
# Hydra Core
---
# About  Core
Hydra is a vocabulary to describe hypermedia-driven Web APIs created by
[Markus Lanthaler](http://www.markus-lanthaler.com/).
It provides the following API primitives:
- Entry point,
- Resource (through RDFS),
- Link (through JSON-LD),
- Affordance (operation),
- Collection of resources (incl. paging),
- API documentation,
- Free text query,
- etc.
---
# Currently in _Unofficial Draft_ state
<iframe src="http://www.hydra-cg.com/spec/latest/core/"></iframe>
---
# Hydra Core by Example (1/2)
Paged collection:
````
{
"@context": "http://www.w3.org/ns/hydra/context.jsonld",
"@id": "http://api.example.com/users/?page=3",
"@type": "PagedCollection",
"totalItems": "4980",
"itemsPerPage": "10",
"firstPage": "/users/?page=1",
"nextPage": "/users/?page=4",
"previousPage": "/users/?page=2",
"lastPage": "/users/?page=498",
"member": [
... the members of this PagedCollection ...
],
"me": "/users/?me"
}
````
---
# Hydra Core by Example (2/2)
Operations:
````
{
"@context": "http://www.w3.org/ns/hydra/context.jsonld",
"@id": "http://api.example.com/an-issue/comments?page=3",
"@type": "PagedCollection",
...
"member": [
... the members of this PagedCollection ...
],
"operation": [
{
"@type": "AppendResourceOperation",
"method": "POST",
"expects": "User"
}