Linked Data Basics


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Linked Data Basics Slot in WWW2012 Tutorial: Practical Cross-Dataset Queries on the Web of Data

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Linked Data Basics

  1. 1. Linked Data Basics Anja Jentzsch, Freie Universität Berlin 17 April 2012Tutorial: Practical Cross-Dataset Queries on the Web of Data WWW2012, Lyon, France 1
  2. 2. Architecture of the classic WebSingle global document space Web Search Browsers EnginesSmall set of simple standards1. HTML as document format2. HTTP URLs as HTML HTML HTML • globally unique IDs hyper- links • retrieval mechanism3. Hyperlinks to connect everything A B C 2
  3. 3. Web 2.0 APIs and MashupsNo single global data spaceShortcomings1. APIs have proprietary interfaces Mashup2. Mashups are based on a fixed set of data sources3. No hyperlinks between data items within Web Web Web Web API API API API different APIs A B C D 3
  4. 4. Web APIs slice the Web into Walled GardensImage: Bob Jagensdorf,, CC-BY 4
  5. 5. Linked DataExtend the Web with a single global data space1. by using RDF to publish structured data on the Web2. by setting links between data items within different data sources RDF RDF RDF RDF RDF RDF RDF RDF RDF RDF RDF RDF RDF RDF Links Links Links Links A B C D E 5
  6. 6. Linked Data PrinciplesSet of best practices for publishing structured data on the Web inaccordance with the general architecture of the Web.1. Use URIs as names for things.2. Use HTTP URIs so that people can look up those names.3. When someone looks up a URI, provide useful RDF information.4. Include RDF statements that link to other URIs so that they can discover related things. Tim Berners-Lee,, 2006 6
  7. 7. The RDF Data Model rdf:typepd:chris foaf:Person foaf:name Chris Bizer foaf:based_near dbpedia:Berlin 7
  8. 8. Data Items are identified with HTTP URIs rdf:type pd:chris foaf:Person foaf:name Chris Bizer foaf:based_near dbpedia:Berlinpd:chris = = 8
  9. 9. Resolving URIs over the Web rdf:typepd:chris foaf:Person foaf:name Chris Bizer 3.450.889 foaf:based_near dp:population dbpedia:Berlin skos:subject dp:Cities_in_Germany 9
  10. 10. Dereferencing URIs over the Web rdf:typepd:chris foaf:Person foaf:name Chris Bizer 3.450.889 foaf:based_near dp:population dbpedia:Berlin skos:subject skos:subject dbpedia:Hamburg dp:Cities_in_Germany skos:subjectdbpedia:Muenchen 10
  11. 11. RDF• RDF is just a data model, it requires a serialization format • For transmission over the network • For storage as files• Multiple serialization formats have been defined • RDF/XML • Turtle • N-Triples • RDFa • ...• It’s all triples! • Syntax doesn’t matter much and can be chosen case-by-case for pragmatic reasons 11
  12. 12. Properties of the Web of Linked Data• Global, distributed data space build on a simple set of standards • RDF, URIs, HTTP• Entities are connected by links • creating a global data graph that spans data sources and • enables the discovery of new data sources• Provides for data-coexistence • Everyone can publish data to the Web of Linked Data • Everyone can express their personal view on things • Everybody can use the vocabularies/schema that they like 12
  13. 13. W3C Linking Open Data Project• Grassroots community effort to • publish existing open license datasets as Linked Data on the Web • interlink things between different data sources 13
  14. 14. LOD Data Sets on the Web: May 2007• 12 data sets• Over 500 million RDF triples• Around 120,000 RDF links between data sources 14
  15. 15. LOD Data Sets on the Web: November 2007• 28 data sets 15
  16. 16. LOD Data Sets on the Web: September 2008• 45 data sets• Over 2 billion RDF triples 16
  17. 17. LOD Data Sets on the Web: July 2009• 95 data sets• Over 6.5 billion RDF triples 17
  18. 18. LOD Data Sets on the Web: September 2010• 203 data sets• Over 24,7 billion RDF triples• Over 436 million RDF links between data sources 18
  19. 19. LOD Data Sets on the Web: September 2011• 295 data sets• Over 31 billion RDF triples• Over 504 million RDF links between data sources 19
  20. 20. LOD Data Set statistics as of 09/2011LOD Cloud Data Catalog on CKAN• statistics• 20
  21. 21. Uptake in the Government Domain• The EU is pushing Linked Data (LOD2, LATC, Eurostat)• W3C Government Linked Data (GLD) Working Group
  22. 22. Uptake in the Libraries Community• Institutions publishing Linked Data • Library of Congress (subject headings) • German National Library (PND dataset and subject headings) • Swedish National Library (Libris - catalog) • Hungarian National Library (OPAC and Digital Library) • British National Library • Europeana project 22
  23. 23. Uptake in the Libraries Community• W3C Library Linked Data Incubator Group (2010)• OKFN Working Group on Bibliographic Data (2010)• Goals: • Integrate Library Catalogs on global scale • Interconnect resources between repositories (by topic, by location, by historical period, by ...) 23
  24. 24. Uptake in the Media Industry • Publish data as RDF or embed as RDFa • Goal: Drive traffic to websites via search engines 24
  25. 25.• jointly proposed vocabularies for embedding data into HTML pages (Microdata)• available since June 2011 25
  26. 26. Linked Data Applications Linked Data Linked Data Search Browsers Mashups EnginesThing Thing Thing Thing ThingThing Thing Thing Thing Thing typed typed typed typed links links links links A B C D E 26
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  30. 30. Lower Data Integration CostsThe overall data integration effort is split betweenthe data publisher, the data consumer and third parties.• Data Publisher • publishes data as RDF • sets identity links • reuses terms or publishes mappings• Third Parties • set identity links pointing at your data • publish mappings to the Web• Data Consumer • has to do the rest • using record linkage and schema matching techniques 30
  31. 31. Is your data 5 star?★ Make your stuff available on the Web (whatever format) under an open license.★★ Make it available as structured data (e.g., Excel instead of image scan of a table) so that it can be reused.★★★ Use non-proprietary, open formats (e.g., CSV instead of Excel).★★★★ Use URIs to identify things, so that people can point at your stuff and serve RDF from it.★ ★ ★ ★ ★ Link your data to other data to provide context. Tim Berners-Lee,, 2010 31
  32. 32. How to publish Linked DataTasks:1. Make data available as RDF via HTTP2. Set RDF links pointing at other data sources3. Make your data self-descriptive4. Reuse common vocabulariesTom Heath, Christian Bizer: Linked Data: Evolving the Web into a Global DataSpace 32
  33. 33. Make Data available as RDF via HTTP•Ready to use tools (examples) • D2R Server • provides for mapping relational databases into RDF and for serving them as Linked Data • Pubby • Linked Data Frontend for SPARQL Endpoints • More tools • CommunityProjects/ LinkingOpenData/PublishingTools 33
  34. 34. Set RDF links to other data sources• Examples of RDF links <> owl:sameAs <http://> . <> foaf:topic_interest <> . <> owl:sameAs <http://> . 34
  35. 35. How to generate RDF links?• Pattern-based approaches • Exploit naming conventions within URIs (for instance ISBNs, ISINs, …)• Similarity-based approaches • Compare items within different data sources using various similarity metrics• Ready to use tools (Examples) • Silk Link Discovery Framework • provides a declarative language for specifying link conditions which may combine different similarity metrics • More tools • EquivalenceMining 35
  36. 36. Make your Data Self-Descriptive• Increase the usefulness of your data and ease data integration• Aspects of self-descriptiveness • Enable clients to retrieve the schema • Reuse terms from common vocabularies • Publish schema mappings for proprietary terms • Provide provenance metadata • Provide licensing metadata • Provide data-set-level metadata using voiD • Refer to additional access methods using voiD 36
  37. 37. Enable Clients to retrieve the Schema Clients can resolve the URIs that identify vocabulary terms in order to get their RDFS or OWL definitions. Some data on the Web <> foaf:name "Richard Cyganiak" ; rdf:type <> . Resolve unknown term RDFS or OWL definition <> rdf:type owl:Class ; rdfs:label "Person"; rdfs:subClassOf <> ; rdfs:subClassOf <> . 37
  38. 38. Reuse Terms from Common Vocabularies• Common Vocabularies • Friend-of-a-Friend for describing people and their social network • SIOC for describing forums and blogs • SKOS for representing topic taxonomies • Organization Ontology for describing the structure of organizations • GoodRelations provides terms for describing products and business entities • Music Ontology for describing artists, albums, and performances • Review Vocabulary provides terms for representing reviews• Common sources of identifiers (URIs) for real world objects • LinkedGeoData and Geonames locations • GeneID and UniProt life science identifiers 38
  39. 39. Linked Data Sets: Distribution of used vocabularies 39
  40. 40. Conclusion• Linked Data provides a standardized data access interface• Linked Data allows for the development of a variety of tools to integrate, enhance and and view the data• The Web of Data is growing rapidly • There are active deployment communities in different domains• Web search is evolving into query answering • Search engines will increasingly rely on structured data from the Web 40
  41. 41. Thanks Questions? Email: Twitter: @anjeveReferences• Tom Heath, Christian Bizer: Linked Data: Evolving the Web into a Global Data Space• Christian Bizer, Tom Heath, Tim Berners-Lee: Linked Data – The Story So Far• Linking Open Data Project Wiki 41