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Linked data

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In computing, linked data (often capitalized as Linked Data) is a method of publishing structured data so that it can be interlinked and become more useful through semantic queries. It builds upon standard Web technologies such as HTTP, RDF and URIs, but rather than using them to serve web pages for human readers, it extends them to share information in a way that can be read automatically by computers. This enables data from different sources to be connected and queried.[1]

Tim Berners-Lee, director of the World Wide Web Consortium (W3C), coined the term in a 2006 design note about the Semantic Web project.[2]

Principles

Tim Berners-Lee outlined four principles of linked data in his "Linked Data" note of 2006,[2] paraphrased along the following lines:

  1. Use URIs to name (identify) things.
  2. Use HTTP URIs so that these things can be looked up (interpreted, "dereferenced").
  3. Provide useful information about what a name identifies when it's looked up, using open standards such as RDF, SPARQL, etc.
  4. Refer to other things using their HTTP URI-based names when publishing data on the Web.

Tim Berners-Lee gave a presentation on linked data at the TED 2009 conference.[3] In it, he restated the linked data principles as three "extremely simple" rules:

  1. All kinds of conceptual things, they have names now that start with HTTP.
  2. If I take one of these HTTP names and I look it up [..] I will get back some data in a standard format which is kind of useful data that somebody might like to know about that thing, about that event.
  3. When I get back that information it's not just got somebody's height and weight and when they were born, it's got relationships. And when it has relationships, whenever it expresses a relationship then the other thing that it's related to is given one of those names that starts with HTTP.

Components

Linked open data

Linked open data is linked data that is open content.[4][5][6] Tim Berners-Lee gives the clearest definition of linked open data in differentiation with linked data. He defines linked data by identifying its four components, and then adds a fifth rule - open content - to define linked open data.[2][7] Large linked open data sets include DBpedia and Freebase.

History

The term "linked open data" has been in use since at least February, 2007, when the "Linking Open Data" mailing list[8] was created.[9] The mailing list was initially hosted by the SIMILE project[10] at the Massachusetts Institute of Technology.

Linking Open Data community project

The above diagram shows which Linking Open Data datasets are connected, as of August 2014. This was produced by the Linked Open Data Cloud project, which was started in 2007. Some sets may include copyrighted data which is freely available.[11]

The goal of the W3C Semantic Web Education and Outreach group's Linking Open Data community project is to extend the Web with a data commons by publishing various open datasets as RDF on the Web and by setting RDF links between data items from different data sources. In October 2007, datasets consisted of over two billion RDF triples, which were interlinked by over two million RDF links.[12][13] By September 2011 this had grown to 31 billion RDF triples, interlinked by around 504 million RDF links. A detailed statistical breakdown was published in 2014.[14]

European Union projects

There are a number of European= Union projects[when defined as?] involving linked data. These include the linked open data around the clock (LATC) project,[15] the PlanetData project,[16] the DaPaaS (Data-and-Platform-as-a-Service) project,[17] and the Linked Open Data 2 (LOD2) project.[18][19][20] Data linking is one of the main goals of the EU Open Data Portal, which makes available thousands of datasets for anyone to reuse and link.

Datasets

  • Wikidata - a collaboratively-created linked dataset that acts as central storage for the structured data of its Wikimedia sister projects
  • DBpedia – a dataset containing extracted data from Wikipedia; it contains about 3.4 million concepts described by 1 billion triples, including abstracts in 11 different languages
  • GeoNames provides RDF descriptions of more than 7,500,000 geographical features worldwide.
  • UMBEL – a lightweight reference structure of 20,000 subject concept classes and their relationships derived from OpenCyc, which can act as binding classes to external data; also has links to 1.5 million named entities from DBpedia and YAGO
  • FOAF – a dataset describing persons, their properties and relationships

Dataset instance and class relationships

Clickable diagrams that show the individual datasets and their relationships within the DBpedia-spawned LOD cloud (as shown by the figures to the right) are available.[21][22]

See also

References

  1. ^ Bizer, Christian; Heath, Tom; Berners-Lee, Tim (2009). "Linked Data—The Story So Far" (PDF). International Journal on Semantic Web and Information Systems. 5 (3): 1–22. doi:10.4018/jswis.2009081901. ISSN 1552-6283. Retrieved 2010-12-18. Solving Semantic Interoperability Conflicts in Cross–Border E–Government Services.
  2. ^ a b c Tim Berners-Lee (2006-07-27). "Linked Data". Design Issues. W3C. Retrieved 2010-12-18.
  3. ^ "Tim Berners-Lee on the next Web".
  4. ^ "Frequently Asked Questions (FAQs) - Linked Data - Connect Distributed Data across the Web".
  5. ^ "COAR » 7 things you should know about…Linked Data".
  6. ^ "Linked Data Basics for Techies".
  7. ^ "Redirecting..." {{cite web}}: Cite uses generic title (help)
  8. ^ "public-lod@w3.org Mail Archives".
  9. ^ "SweoIG/TaskForces/CommunityProjects/LinkingOpenData/NewsArchive".
  10. ^ "SIMILE Project - Mailing Lists".
  11. ^ Linking open data cloud diagram 2014, by Max Schmachtenberg, Christian Bizer, Anja Jentzsch and Richard Cyganiak. http://lod-cloud.net/
  12. ^ Linking Open Data
  13. ^ Fensel, Dieter; Facca, Federico Michele; Simperl, Elena; Ioan, Toma (2011). Semantic Web Services. Springer. p. 99. ISBN 3642191924.
  14. ^ http://linkeddatacatalog.dws.informatik.uni-mannheim.de/state/
  15. ^ Linked open data around the clock (LATC)
  16. ^ PlanetData
  17. ^ DaPaaS
  18. ^ Linking Open Data 2 (LOD2)
  19. ^ "CORDIS FP7 ICT Projects – LOD2". European Commission. 2010-04-20.
  20. ^ "LOD2 Project Fact Sheet – Project Summary" (PDF). 2010-09-01. Retrieved 2010-12-18.
  21. ^ Instance relationships amongst datasets
  22. ^ Class relationships amongst datasets

Further reading

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