What is Linked Data?

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What is Linked Data? Presented at the Linked Data for Libraries on Thursday, November 6, 2014 at Trinity College Dublin http://www.dri.ie/linked-data-libraries

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  • 1. What is Linked Data?Linked Data for Libraries, 6th Nov 2014, Royal Irish AcademyDr.ChristopheDebruyneDigitalRepositoryofIrelandRoyalIrishAcademyInsightCentreofDataAnaly

2. What is Linked Data? Linked Data started off as a initiative called the LinkingOpen Data (LOD) project. Linked Data is a global initiative to publish and interlinkstructured data on the Web using a combination of wellestablished technologies. Uniform Resource Identifiers to name things; Resource Description Framework to represent things; HTTP infrastructure to obtain those representations.Linked Data for Librarians November 6, 2014 Royal Irish Academy 3. Web of Documents vs. Web of Data The Web of Documents were created by humans forhumans; the links between documents bore littlemeaning for machines and documents provided littlestructured information. Structured information can be found on the Web suchas XML, CSV, etc. but, How do we link data rather than documents, and createa global database of information?Linked Data for Librarians November 6, 2014 Royal Irish Academy 4. Towards a Web of Documents We need appropriate methods (guidelines) andLinked Data for Librarians November 6, 2014 Royal Irish Academystandards. Tim Berners-Lee formulated four rules for creatingand publishing Linked Data on the Web. 5. Linked Data for Librarians November 6, 2014 Royal Irish AcademyThe four principlesNumber1UseURIsasnamesforthings. 6. (1) Use URIs to name things Use Uniform Resource Identifiers (URIs) to nameeverything you need to describe on the Web People, geographical locations, books, Events, emotion, religion, Linked Data for Librarians November 6, 2014 Royal Irish Academy Examples http://dbpedia.org/resource/James_Joyce ftp://example.org/file.txt urn:ISSN:1535-3613 But 7. Linked Data for Librarians November 6, 2014 Royal Irish AcademyThe four principlesNumber1UseURIsasnamesforthings.Number2UseHTTPURIssothatpeoplecanlookupthosenames. 8. (2) Use HTTP URIs to look up those names HTTP URIs allow one to reuse the existing HTTPinfrastructure to return something when oneperforms an HTTP GET request. One can for instance put the HTTP URI in abrowsers address bar and hopefully get aresult. http://dbpedia.org/resource/James_JoyceLinked Data for Librarians November 6, 2014 Royal Irish Academy 9. Linked Data for Librarians November 6, 2014 Royal Irish AcademyThe four principlesNumber1UseURIsasnamesforthings.Number2UseHTTPURIssothatpeoplecanlookupthosenames.Number3WhensomeonelooksupaURI,provideusefulinformaJoyce, James Augustine AloysiusLinked Data for Librarians November 6, 2014 Royal Irish Academy 13. foaf:nameLinked Data for Librarians November 6, 2014 Royal Irish Academyfoaf:based_near 14. Ontologies An ontology is an explicit [formal] specification of a [shared]conceptualization. (Gruber, 1993) RDF is the data model. RDF, RDFS and OWL are ontology languages. RDF Declare types and relations; RDFS Declare type- & role hierarchies, domains and rages, etc. OWL Properties of relations, Disjointness, etc. Popular ontologies for instance are Friend-of-a-Friend (FOAF),Simple Knowledge Organization System (SKOS), Dublin Core terms Ontologies allows us to describe resources.Linked Data for Librarians November 6, 2014 Royal Irish Academy 15. Information resources and non-information resources Information resources are documents referred to by aURI that describe non-information resources namedwith a URI that represent things such as cars, people,etc. The NIR http://dbpedia.org/resource/James_Joyce isdescribed by the following IRs: The web page http://dbpedia.org/page/James_Joyce The RDF doc http://dbpedia.org/data/James_Joyce Either is returned depending on what you need. How?Linked Data for Librarians November 6, 2014 Royal Irish Academy 16. Content negotiation part of the HTTP infrastructureResource identifiers: HTTP URIs not only as a name, but also for a Web look-up. Non-information resources can have multiple representations:HTML, RDF/XML, ...HTTP URI dereferencing: To dereference To obtain the address of a data item heldin another location from a pointer URI pointing to a IR returns the representation. URI pointing to a NIR returns a redirect to an IR describingthat NIR.Linked Data for Librarians November 6, 2014 Royal Irish Academy 17. Linked Data for Librarians November 6, 2014 Royal Irish AcademyContent negotiationImagefromhSp://www.w3.org/TR/swbp-vocab-pub/ 18. What should be returned? RDF should be at least be represented as RDF/XML. All RDF triples with the NIRs URI as the subject in thetriples. Triples where the NIR is a object are optional,but nice to have. Descriptions about related resources and metadata(e.g. publisher, creation date, etc.) should be attachedto the information resource.Linked Data for Librarians November 6, 2014 Royal Irish Academy 19. Content negotiation in Linked LogainmLinked Logainm is a collaborative project undertakenby the DRI, Insight @ NUI Galway, Fiontar at DCU, theNational Library of Ireland and the Placenames Branchof the Department of Arts, Heritage and the Gaeltacht.The Linked Logainm project has created a new opendataset, which allows Irish place names to be linkedacross the world by cutting edge technologiesdeveloped in Ireland.Linked Data for Librarians November 6, 2014 Royal Irish Academy 20. Content negotiation in Linked LogainmWestport is identified by the URI http://data.logainm.ie/place/132920$ curl -H "Accept:text/rdf+n3" http://data.logainm.ie/place/13292@prefix rdf: .@prefix spatial: . rdf:typespatial:Feature .@prefix ns2: . rdf:type ns2:B .@prefix owl: .@prefix ns4: . owl:sameAsns4:node52244000 , , .@prefix foaf: . foaf:name "Westport"@enLinked Data for Librarians November 6, 2014 Royal Irish Academy 21. Linked Data for Librarians November 6, 2014 Royal Irish AcademyThe four principlesNumber1UseURIsasnamesforthings.Number2UseHTTPURIssothatpeoplecanlookupthosenames.Number3WhensomeonelooksupaURI,provideusefulinformadbpedia-owl:birthPlace . But also across datasetsowl:sameAs .Linked Data for Librarians November 6, 2014 Royal Irish Academy 23. Example of linking across datasetsdbpedia-owl:popula