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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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What is Linked Data?

  1. 1. What is Linked Data? Linked Data for Libraries, 6th Nov 2014, Royal Irish Academy Dr. Christophe Debruyne Digital Repository of Ireland – Royal Irish Academy Insight Centre of Data Analy<cs – NUI Galway Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  2. 2. What is Linked Data? • Linked Data started off as a initiative called the Linking Open Data (LOD) project. • Linked Data is a global initiative to publish and interlink structured data on the Web using a combination of well established 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. 3. Web of Documents vs. Web of Data • The Web of Documents were created by humans for humans; the links between documents bore little meaning for machines and documents provided little structured information. • Structured information can be found on the Web – such as XML, CSV, etc. – but, … • How do we link data rather than documents, and create a global “database” of information? Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  4. 4. Towards a Web of Documents • We need appropriate methods (guidelines) and Linked Data for Librarians – November 6, 2014 – Royal Irish Academy standards. • Tim Berners-Lee formulated four rules for creating and publishing Linked Data on the Web.
  5. 5. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy The four principles Number 1 “Use URIs as names for things.”
  6. 6. (1) Use URIs to name things • Use Uniform Resource Identifiers (URIs) to name everything 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. 7. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy The four principles Number 1 “Use URIs as names for things.” Number 2 “Use HTTP URIs so that people can look up those names.”
  8. 8. (2) Use HTTP URIs to look up those names • HTTP URIs allow one to reuse the existing HTTP infrastructure to return something when one performs an HTTP GET request. • One can for instance put the HTTP URI in a browser’s address bar and – hopefully – get a result. • http://dbpedia.org/resource/James_Joyce Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  9. 9. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy The four principles Number 1 “Use URIs as names for things.” Number 2 “Use HTTP URIs so that people can look up those names.” Number 3 “When someone looks up a URI, provide useful informa<on, using the standards (RDF, SPARQL)”
  10. 10. (3) Provide useful Information for URI look-ups • When entities are identified by URIs that use the http:// scheme, these entities can be looked up simply by dereferencing the URI over the HTTP protocol. • Simple, standardized mechanism for retrieving resources via these URIs. • Provide information suitable for the “consumer” • Humans rather see HTML pages, PDFs, pictures, … • Machines want machine-readable formats such as RDF Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  11. 11. Resource Description Framework • RDF is not (really) a language but a model (!!!) • RDF is a W3C recommendation • RDF is designed to be read by computers • RDF is for describing resources on the Web in terms of triples (subject – predicate – object) • RDF uses URIs to identify and reference resources on Linked Data for Librarians – November 6, 2014 – Royal Irish Academy the Web • RDF/XML is just one way of serializing RDF • Others are Turtle, N3, etc.
  12. 12. Resource Description Framework <?xml version="1.0" encoding="utf-8" ?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:foaf="http://xmlns.com/foaf/0.1/" > <rdf:Description rdf:about="http://dbpedia.org/resource/James_Joyce"> <foaf:name>Joyce, James Augustine Aloysius</foaf:name> <foaf:based_near rdf:resource="http://dbpedia.org/resource/Zurich" /> Linked Data for Librarians – November 6, 2014 – Royal Irish Academy </rdf:Description> </rdf:RDF>
  13. 13. foaf:name Linked Data for Librarians – November 6, 2014 – Royal Irish Academy foaf:based_near
  14. 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 à Declare types and relations; • RDFS à Declare type- & role hierarchies, domains and rages, etc. • OWL à 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. 15. Information resources and non-information resources • Information resources are documents – referred to by a URI – that describe non-information resources – named with a URI – that represent things such as cars, people, etc. • The NIR http://dbpedia.org/resource/James_Joyce is described 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. 16. Content negotiation – part of the HTTP infrastructure Resource 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 held in another location from a pointer” • URI pointing to a IR returns the representation. • URI pointing to a NIR returns a redirect to an IR describing that NIR. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  17. 17. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy Content negotiation Image from hSp://www.w3.org/TR/swbp-­‐vocab-­‐pub/
  18. 18. What should be returned? • RDF should be at least be represented as RDF/XML. • All RDF triples with the NIR’s URI as the subject in the triples. 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 attached to the information resource. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  19. 19. Content negotiation in Linked Logainm Linked Logainm is a collaborative project undertaken by the DRI, Insight @ NUI Galway, Fiontar at DCU, the National Library of Ireland and the Placenames Branch of the Department of Arts, Heritage and the Gaeltacht. The Linked Logainm project has created a new open dataset, which allows Irish place names to be linked across the world by cutting edge technologies developed in Ireland. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  20. 20. Content negotiation in Linked Logainm Westport 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: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix spatial: <http://geovocab.org/spatial#> . <http://data.logainm.ie/place/132920> rdf:type spatial:Feature . @prefix ns2: <http://data.logainm.ie/category/> . <http://data.logainm.ie/place/132920> rdf:type ns2:B . @prefix owl: <http://www.w3.org/2002/07/owl#> . @prefix ns4: <http://linkedgeodata.org/triplify/> . <http://data.logainm.ie/place/132920> owl:sameAs ns4:node52244000 , <http://id.worldcat.org/fast/1210744> , <http://sws.geonames.org/2960970/> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . <http://data.logainm.ie/place/132920> foaf:name "Westport"@en … Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  21. 21. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy The four principles Number 1 “Use URIs as names for things.” Number 2 “Use HTTP URIs so that people can look up those names.” Number 3 “When someone looks up a URI, provide useful informa<on, using the standards (RDF, SPARQL)” Number 4 “Include links to other URIs, so that they can discover more things.”
  22. 22. (4) Include links to other URIs • Not only within the same dataset <http://dbpedia.org/resource/James_Joyce> dbpedia-owl:birthPlace <http://dbpedia.org/resource/Dublin"> . • But also across datasets <http://dbpedia.org/page/Dublin> owl:sameAs <http://sws.geonames.org/7778677/> . Linked Data for Librarians – November 6, 2014 – Royal Irish Academy
  23. 23. Example of linking across datasets dbpedia-­‐owl:popula<onTotal gn:popula<on gn:name Linked Data for Librarians – November 6, 2014 – Royal Irish Academy hSp:// dbpedia.org/ resource/Dublin Dublin rdfs:label 527612 owl:sameAs hSp:// sws.geonames.org /7778677/ hSp:// sws.geonames.org /7778677/ 527612 Dublin City
  24. 24. Linked Data for Librarians – November 6, 2014 Linking Open Data cloud diagram 2014, by Max Schmachten b–e Rrogy,a lC Irhisrhi sA<caadnem Byi zer, Anja Jentzsch and Richard Cyganiak. hSp://lod-­‐cloud.net/
  25. 25. References • Berners-Lee, T. (2006). Linked Data - Design Issues. Retrieved October 20 2014, http://www.w3.org/ DesignIssues/LinkedData.html • Gruber, T. R. (1993) Towards principles for the design of ontologies used for knowledge sharing. In Guarino, N. and Poli, R., eds. Formal Ontology in Conceptual Analysis and Knowledge representation. Kluwer Academic Publishers, Deventer, The Netherlands. • Hitzler, P., Krotzsch, M., and Rudolph, S. (2010) Foundations of Semantic Web Technologies. CRC Press, Boca Raton, FL, the US. • van Hooland, S. and Verborgh, R. (2014) Linked Data for Libraries, Archives and Museums. How to clean, link and publish your metadata. Facet Publishing, London, The UK. Linked Data for Librarians – November 6, 2014 – Royal Irish Academy

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