In computing, linked data is structured data which is associated with ("linked" to) other data. Interlinking makes the data more useful through semantic queries. Tim Berners-Lee, director of the World Wide Web Consortium (W3C), coined the term in a 2006 design note about the Semantic Web project. Part of the vision of linked data is for the Internet to become a global database.

Linked data builds upon standard Web technologies such as HTTP, RDF and URIs, but rather than using them to serve web pages and hyperlinks only for human readers, it extends them to share information in a way that can be read automatically by computers (machine readable). Linked data may also be open data, in which case it is usually described as Linked Open Data.

Principles

In his 2006 "Linked Data" note, Tim Berners-Lee outlined four principles of linked data, paraphrased along the following lines:[1]

  1. Uniform Resource Identifiers (URIs) should be used to name and identify individual things.
  2. HTTP URIs should be used to allow these things to be looked up, interpreted, and subsequently "dereferenced".
  3. Useful information about what a name identifies should be provided through open standards such as RDF, SPARQL, etc.
  4. When publishing data on the Web, other things should be referred to using their HTTP URI-based names.

Tim Berners-Lee later restated these principles at a 2009 TED conference, again paraphrased along the following lines:[2]

  1. All conceptual things should have a name starting with HTTP.
  2. Looking up an HTTP name should return useful data about the thing in question in a standard format.
  3. Anything else that that same thing has a relationship with through its data should also be given a name beginning with HTTP.

Components

Thus, we can identify the following components as essential to a global Linked Data system as envisioned, and to any actual Linked Data subset within it:

Linked open data

Linked open data are linked data that are open data.[4][5][6] Tim Berners-Lee gives the clearest definition of linked open data as differentiated from linked data.

Linked Open Data (LOD) is Linked Data which is released under an open license, which does not impede its reuse for free.

— Tim Berners-Lee, Linked Data[1][7]

Large linked open data sets include DBpedia, Wikibase, Wikidata and Open ICEcat.

5-star linked open data

In 2010, Tim Berners-Lee suggested a 5-star scheme for grading the quality of open data on the web, for which the highest ranking is Linked Open Data:[9]

History

The term "linked open data" has been in use since at least February 2007, when the "Linking Open Data" mailing list[10] was created.[11] The mailing list was initially hosted by the SIMILE project[12] at the Massachusetts Institute of Technology.

Linking Open Data community project

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.[14][15] 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.[16]

European Union projects

There are a number of European Union projects involving linked data. These include the linked open data around the clock (LATC) project,[17] the AKN4EU project for machine-readable legislative data,[18] the PlanetData project,[19] the DaPaaS (Data-and-Platform-as-a-Service) project,[20] and the Linked Open Data 2 (LOD2) project.[21][22][23] 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.

Ontologies

Ontologies are formal descriptions of data structures. Some of the better known ontologies are:

Datasets

Dataset instance and class relationships

Clickable diagrams that show the individual datasets and their relationships within the DBpedia-spawned LOD cloud (as by the figures to the right) are available.[28][29]

See also

References

  1. Tim Berners-Lee (2006-07-27). "Linked Data". Design Issues. W3C.
  2. "Tim Berners-Lee on the next Web". Archived from the original on 2011-04-10.
  3. "CSV on the Web Working Group Wiki".
  4. "Frequently Asked Questions (FAQs) - Linked Data - Connect Distributed Data across the Web". Archived from the original on 2015-11-18.
  5. "COAR » 7 things you should know about…Linked Data". Archived from the original on 2015-11-18.
  6. "Linked Data Basics for Techies". Archived from the original on 2021-05-05.
  7. "5 Star Open Data".
  8. "5-star Open Data". 5stardata.info.
  9. "What is 5 Star Linked Data? | Webize Everything Community Group". www.w3.org. 17 January 2014.
  10. "public-lod@w3.org Mail Archives".
  11. "SweoIG/TaskForces/CommunityProjects/LinkingOpenData/NewsArchive".
  12. "SIMILE Project - Mailing Lists".
  13. Linking open data cloud diagram 2014, by Max Schmachtenberg, Christian Bizer, Anja Jentzsch and Richard Cyganiak. https://lod-cloud.net/
  14. "SweoIG/TaskForces/CommunityProjects/LinkingOpenData - W3C Wiki". esw.w3.org. Archived from the original on 16 November 2009.
  15. Fensel, Dieter; Facca, Federico Michele; Simperl, Elena; Ioan, Toma (2011). Semantic Web Services. Springer. p. 99. ISBN 978-3642191923.
  16. Max. "State of the LOD Cloud". linkeddatacatalog.dws.informatik.uni-mannheim.de.
  17. "Linked open data around the clock (LATC)". latc-project.eu. Archived from the original on 19 September 2018.
  18. Flatt, Amelie; Langner, Arne; Leps, Olof (2022), "Model-Driven Development of AKN Application Profiles: Background and Requirements", Model-Driven Development of Akoma Ntoso Application Profiles, Cham: Springer International Publishing, pp. 5–12, doi:10.1007/978-3-031-14132-4_2, ISBN 978-3-031-14131-7{{citation}}: CS1 maint: work parameter with ISBN (link)
  19. "Welcome to PlanetData! - PlanetData". planet-data.eu. Archived from the original on 21 April 2021.
  20. "DaPaaS". project.dapaas.eu. Archived from the original on 18 December 2020.
  21. Linking Open Data 2 (LOD2)
  22. "CORDIS FP7 ICT Projects – LOD2". European Commission. 2010-04-20.
  23. "LOD2 Project Fact Sheet – Project Summary" (PDF). 2010-09-01. Archived from the original (PDF) on 2011-07-20.
  24. "GRID Statistics". grid.ac/stats.
  25. "GRID Policies". grid.ac.
  26. "KnowWhereGraph". knowwheregraph.org.
  27. Krzysztof Janowicz; Pascal Hitzler; Wenwen Li; Dean Rehberger; Mark Schildhauer; Rui Zhu; Cogan Shimizu; Colby K. Fisher; Ling Cai; Gengchen Mai; Joseph Zalewski; Lu Zhou; Shirly Stephen; Seila Gonzalez Estrecha; Bryce D. Mecum; Anna Lopez-Carr; Andrew Schroeder; Dave Smith; Dawn J. Wright; Sizhe Wang; Yuanyuan Tian; Zilong Liu; Meilin Shi; Anthony D'Onofrio; Zhining G; Kitty Currier (2022). "Know, Know Where, Knowwheregraph: A Densely Connected, Cross-Domain Knowledge Graph and Geo-Enrichment Service Stack for Applications in Environmental Intelligence". AI Magazine. 43 (1): 30–39. doi:10.1609/aimag.v43i1.19120. hdl:1983/be176aba-9dec-456c-9615-01a0e8556b7b.
  28. "Instance relationships amongst datasets". fu-berlin.de. Archived from the original on 2012-10-17.
  29. "Class relationships amongst datasets". Archived from the original on 28 August 2011.

Further reading