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JSON-LD Linked Data for Web Apps Gregg Kellogg gregg@greggkellogg.net @gkelloggTuesday, July 10, 12

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Introducing JSON-LD @graph @context @id JSON-based syntax to express linked data @language @value @list @type @setTuesday, July 10, 12JSON-LD brings a standard representation for expressing entity-value relationships using afew 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.

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Self-describing Messages • Give objects types { "@context": { (@type) "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, 12The @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.

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Self-describing Messages • Give objects types { "@context": { (@type) "schema": "http://schema.org/", "Person": "schema:Person", • "knows": {"@id": "schema:knows", "@type": "@id"}, Associate properties "name": "schema:name", "image": {"@id": "schema:image", "@type": "@id"}, with IRIs "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

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Self-describing Messages • Give objects types { "@context": { (@type) "schema": "http://schema.org/", "Person": "schema:Person", • "knows": {"@id": "schema:knows", "@type": "@id"}, Associate properties "name": "schema:name", "image": {"@id": "schema:image", "@type": "@id"}, with IRIs "url": {"@id": "schema:url", "@type": "@id"} } • } Use terms defined in a referenced context { "@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

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

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

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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 DataTuesday, July 10, 12

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

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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 FPWDTuesday, July 10, 12

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Language PrinciplesTuesday, July 10, 12

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

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

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

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

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

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

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• { Define referenced subject "@context": "http://json-ld.org/contexts/person", definition with chaining "@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, 12Subject reference identifies an object with @id in the same document, or references anexternal document (Linked Data).

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• { Define referenced subject "@context": "http://json-ld.org/contexts/person", definition with chaining "@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", • Add @language to values. "@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, 12Subject reference identifies an object with @id in the same document, or references anexternal document (Linked Data).

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

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• Add property @type and { "@context": { @language definitions to "schema": "http://schema.org/", context "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

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• 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-syntaxTuesday, July 10, 12

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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, 12Normal JSON can be made JSON-LD by adding an external context through an HTTP linkrelation.

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

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

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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/toRDFTuesday, July 10, 12

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More Information json-ld.org JavaScript Ruby w3c Python PHP Java Gregg Kellogg C++ gregg@greggkellogg.net http://greggkellogg.net/ @gkelloggTuesday, July 10, 12