JSON-LD: Linked Data for Web Apps

1. JSON-LD
Linked Data for Web Apps
Gregg Kellogg
[email protected]
@gkellogg
Tuesday, July 10, 12

2. Introducing JSON-LD
JSON-based syntax to express linked data
@context
@id
@type
@value
@language
@graph
@list
@set
Tuesday, July 10, 12
JSON-LD brings a standard representation for expressing entity-value relationships using a
few standard keywords and a consistent organizational structure for JSON Objects.
•Objects represent entities, with keys acting as properties.
•Properties always expand to full IRIs.
•Arrays express a set of values associated with a property, unordered by default.
•Order expressed in @context or as an expanded value representation.
•Values are Object, string or native, with standard XSD representations for native types.
•Expanded form allows for more datatype and language variations.

3. Self-describing Messages
•
Give objects types
(@type)
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"knows": {"@id": "schema:knows", "@type": "@id"},
"name": "schema:name",
"image": {"@id": "schema:image", "@type": "@id"},
"url": {"@id": "schema:url", "@type": "@id"}
}
}
{
"@context": "http://example.com/context.jsonld",
"@type": "Person",
"image": "http://localhost:9393/examples/schema.org/janedoe.jpg",
"knows": [
"http://www.xyz.edu/students/alicejones.html",
"http://www.xyz.edu/students/bobsmith.html"
],
"name": "Jane Doe",
"url": "http://www.janedoe.com"
}
Tuesday, July 10, 12
The @type key gives an object with one or more types, described with an IRI.
The @context provides a way to express IRIs as simple terms, and allows values to be typed.

4. Self-describing Messages
•
Give objects types
(@type)
•
Associate properties
with IRIs
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"knows": {"@id": "schema:knows", "@type": "@id"},
"name": "schema:name",
"image": {"@id": "schema:image", "@type": "@id"},
"url": {"@id": "schema:url", "@type": "@id"}
}
}
{
"@context": "http://example.com/context.jsonld",
"@type": "Person",
"image": "http://localhost:9393/examples/schema.org/janedoe.jpg",
"knows": [
"http://www.xyz.edu/students/alicejones.html",
"http://www.xyz.edu/students/bobsmith.html"
],
"name": "Jane Doe",
"url": "http://www.janedoe.com"
}
Tuesday, July 10, 12

5. Self-describing Messages
•
Give objects types
(@type)
•
Associate properties
with IRIs
•
Use terms defined in a
referenced context
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"knows": {"@id": "schema:knows", "@type": "@id"},
"name": "schema:name",
"image": {"@id": "schema:image", "@type": "@id"},
"url": {"@id": "schema:url", "@type": "@id"}
}
}
{
"@context": "http://example.com/context.jsonld",
"@type": "Person",
"image": "http://localhost:9393/examples/schema.org/janedoe.jpg",
"knows": [
"http://www.xyz.edu/students/alicejones.html",
"http://www.xyz.edu/students/bobsmith.html"
],
"name": "Jane Doe",
"url": "http://www.janedoe.com"
}
Tuesday, July 10, 12

6. Self-describing Messages
•
Give objects types
(@type)
•
Associate properties
with IRIs
•
Use terms defined in a
referenced context
•
Specify property types
in context
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"knows": {"@id": "schema:knows", "@type": "@id"},
"name": "schema:name",
"image": {"@id": "schema:image", "@type": "@id"},
"url": {"@id": "schema:url", "@type": "@id"}
}
}
{
"@context": "http://example.com/context.jsonld",
"@type": "Person",
"image": "http://localhost:9393/examples/schema.org/janedoe.jpg",
"knows": [
"http://www.xyz.edu/students/alicejones.html",
"http://www.xyz.edu/students/bobsmith.html"
],
"name": "Jane Doe",
"url": "http://www.janedoe.com"
}
Tuesday, July 10, 12

7. RDF Mapping
{
"@context": {
"schema": "http://schema.org/",
"schema:knows": {"@type": "@id"},
"schema:image": {"@type": "@id"},
"schema:url": {"@type": "@id"}
}
}
{
"@context": "http://example.com/context.jsonld",
"@type": "schema:Person",
"schema:image":
"http://localhost:9393/examples/schema.org/janedoe.jpg",
"schema:knows": [
"http://www.xyz.edu/students/alicejones.html",
"http://www.xyz.edu/students/bobsmith.html"
],
"schema:name": "Jane Doe",
"schema:url": "http://www.janedoe.com"
}
@prefix schema: <http://schema.org/> .
[ a schema:Person;
schema:image
<http://localhost:9393/examples/schema.org/janedoe.jpg >;
schema:knows
<http://www.xyz.edu/students/alicejones.html>,
<http://www.xyz.edu/students/bobsmith.html>;
schema:name “Jane Doe”;
schema:url <http://www.janedoe.com>
] .
Tuesday, July 10, 12

8. History
•
2010 – Started as a way to project from the RDFa API
•
Developers want solutions to work within HTML
applications
•
Desire for JSON-idiomatic way of representing RDF
(Linked Data)
•
Adapt existing JSON APIs to Linked Data
Tuesday, July 10, 12

9. History
•2011 – W3C Community Group launched
•Broad Participation
•Separation of Syntax from API
•Proposed to W3C RDF 1.1 Working
Group
Tuesday, July 10, 12

10. History
•2012 – RDF WG abandons other JSON
serialization efforts (RDF/JSON)
•JSON-LD accepted as official work item
•Community Group drafts final report
•RDF WG to publish JSON-LD (Syntax
and API) as FPWD
Tuesday, July 10, 12

11. Language Principles
Tuesday, July 10, 12

12. {
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
•
Make full use of JSON syntactic
representations
•
Object defines a subject
definition
Tuesday, July 10, 12

13. {
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
•
Make full use of JSON syntactic
representations
•
Object defines a subject
definition
{ "@id": "http://greggkellogg.net/foaf#me" }
•
Also used for subject
reference and value
representations
Tuesday, July 10, 12

14. {
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
•
Make full use of JSON syntactic
representations
•
Object defines a subject
definition
{ "@id": "http://greggkellogg.net/foaf#me" }
•
Also used for subject
reference and value
representations
•
Arrays describe sets of unordered
values
•
Single values can skip array
{
"@type": "Recipe",
"name": "Mom's World Famous Banana Bread",
"ingredients": [
"3 or 4 ripe bananas, smashed",
"1 egg",
"3/4 cup of sugar"
],
"nutrition": [{
"@type": ["NutritionInformation"],
"calories": ["240 calories"],
"fatContent": ["9 grams fat"]
}]
}
Tuesday, July 10, 12

15. {
"@id": "http://greggkellogg.net/foaf#me",
"@type": "http://schema.org/Person",
"http://schema.org/name": "Gregg Kellogg",
"http://schema.org/knows": {
"@id": "http://www.markus-lanthaler.com/"
}
}
•
Define terms to use short
property names
•
Convenient for JavaScript “.”
notation
{
"@context": {
"Person": "http://schema.org/Person",
"name": "http://schema.org/name",
"knows”: "http://schema.org/knows"
},
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": {"@id": "http://www.markus-lanthaler.com/"}
}
Tuesday, July 10, 12

16. •
Define terms to use short
property names
•
Convenient for JavaScript “.”
notation
•
Add @type coercions to
use simple string value.
{
"@id": "http://greggkellogg.net/foaf#me",
"@type": "http://schema.org/Person",
"http://schema.org/name": "Gregg Kellogg",
"http://schema.org/knows": {
"@id": "http://www.markus-lanthaler.com/"
}
}
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"name": "schema:name",
"knows”: {
"@id": "schema:knows",
"@type": "@id"
},
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
Tuesday, July 10, 12

17. •
Define terms to use short
property names
•
Convenient for JavaScript “.”
notation
•
Add @type coercions to
use simple string value.
{
"@id": "http://greggkellogg.net/foaf#me",
"@type": "http://schema.org/Person",
"http://schema.org/name": "Gregg Kellogg",
"http://schema.org/knows": {
"@id": "http://www.markus-lanthaler.com/"
}
}
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"name": "schema:name",
"knows”: {
"@id": "schema:knows",
"@type": "@id"
}
}
•
Use external @context.
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
Tuesday, July 10, 12

18. •
Define referenced subject
definition with chaining
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": {
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"knows" "http://greggkellogg.net/foaf#me"
}
}
Tuesday, July 10, 12
Subject reference identifies an object with @id in the same document, or references an
external document (Linked Data).

19. •
Define referenced subject
definition with chaining
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": {
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"knows" "http://greggkellogg.net/foaf#me"
}
}
•
Add @language to values.{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"honorificSuffix": {"@value": "M.S.", "@language": "en"},
"knows": {
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"honorificSuffix": {"@value": "Dipl.Ing.", "@language": "de"},
"knows" "http://greggkellogg.net/foaf#me"
}
}
Tuesday, July 10, 12
Subject reference identifies an object with @id in the same document, or references an
external document (Linked Data).

20. •
Add @type to values.
•
Link to externally defined
resources.
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"birthDate": {"@value": "1957-02-27", "@type": "xsd:date"},
"honorificSuffix": {"@value": "M.S.", "@language": "en"},
"knows": "http://www.markus-lanthaler.com/"
}
Tuesday, July 10, 12

21. •
Add property @type and
@language definitions to
context
{
"@context": {
"schema": "http://schema.org/",
"Person": "schema:Person",
"name": "schema:name",
"birthDate”: {
"@id": "schema: birthDate","@type": "xsd:date"
},
"honorificSuffix”: {
"@id": "schema:honorificSuffix","@language": "en"
},
"knows”: {"@id": "schema:knows","@type": "@id"}
},
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"birthDate": "1957-02-27",
"honorificSuffix": "M.S.",
"knows": "http://www.markus-lanthaler.com/"
}
Tuesday, July 10, 12

22. •More features defined in the syntax
specification*:
•@set, @list, Compact IRIs, Unlabeled
Nodes
•Embedded @context definitions
•Named Graphs
* http://json-ld.org/spec/latest/json-ld-syntax
Tuesday, July 10, 12

23. Retrofit existing APIs
GET /foaf.json HTTP/1.1
Host: greggkellogg.net
Accept: application/json,*/*;q=0.1
====================================
HTTP/1.0 200 OK
...
Content-Type: application/json
Link: <http://json-ld.org/contexts/person>; rel="describedby"; type="application/ld+json"
{
"name": "Gregg Kellogg",
"homepage": "http://greggkellogg.net/",
"depiction": "http://twitter.com/account/profile_image/gkellogg"
}
Tuesday, July 10, 12
Normal JSON can be made JSON-LD by adding an external context through an HTTP link
relation.

24. The “LD” in JSON-LD
•
IRIs are first-class
citizens
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
http://greggkellogg.net/foaf
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"knows" "http://greggkellogg.net/foaf#me"
}
http://www.markus-lanthaler.com
Tuesday, July 10, 12

25. The “LD” in JSON-LD
•
IRIs are first-class
citizens
•
Object definitions may
be referenced or
embedded
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": {
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"knows" "http://greggkellogg.net/foaf#me"
}
} {
"@context": "http://json-ld.org/contexts/person",
"@id": "http://greggkellogg.net/foaf#me",
"@type": "Person",
"name": "Gregg Kellogg",
"knows": "http://www.markus-lanthaler.com/"
}
http://greggkellogg.net/foaf
{
"@context": "http://json-ld.org/contexts/person",
"@id": "http://www.markus-lanthaler.com/",
"@type": "Person",
"name": "Markus Lanthaler",
"knows" "http://greggkellogg.net/foaf#me"
}
http://www.markus-lanthaler.com
Tuesday, July 10, 12

26. JSON-LD API
•compact – use minimal representation
using a supplied @context
•expand – expand to full form, removing
embedded @context definitions
•frame – query for JSON-LD
•fromRDF/toRDF
Tuesday, July 10, 12

27. More Information
json-ld.org
w3c
JavaScript
Ruby
Python
Java
C++
PHP
Gregg Kellogg
@gkellogg
[email protected]
http://greggkellogg.net/
Tuesday, July 10, 12