From Chaos, Order: W3C Standard Helps Organize Knowledge

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SKOS Connects Diverse Knowledge Organization Systems to Linked Data

Testimonials -- 18 August 2009 -- Today W3C announces a new standard that builds a bridge between the world of knowledge organization systems — including thesauri, classifications, subject headings, taxonomies, and folksonomies — and the linked data community, bringing benefits to both. Libraries, museums, newspapers, government portals, enterprises, social networking applications, and other communities that manage large collections of books, historical artifacts, news reports, business glossaries, blog entries, and other items can now use Simple Knowledge Organization System (SKOS) to leverage the power of linked data. As different communities with expertise and established vocabularies use SKOS to integrate them into the Semantic Web, they increase the value of the information for everyone.

SKOS Adapts to the Diversity of Knowledge Organization Systems

A useful starting point for understanding the role of SKOS is the set of subject headings published by the US Library of Congress (LOC) for categorizing books, videos, and other library resources. These headings can be used to broaden or narrow queries for discovering resources. For instance, one can narrow a query about books on "Chinese literature" to "Chinese drama," or further still to "Chinese children's plays."

Library of Congress subject headings have evolved within a community of practice over a period of decades. By now publishing these subject headings in SKOS, the Library of Congress has made them available to the linked data community, which benefits from a time-tested set of concepts to re-use in their own data. This re-use adds value ("the network effect") to the collection. When people all over the Web re-use the same LOC concept for "Chinese drama," or a concept from some other vocabulary linked to it, this creates many new routes to the discovery of information, and increases the chances that relevant items will be found. As an example of mapping one vocabulary to another, a combined effort from the STITCH, TELplus and MACS Projects provides links between LOC concepts and RAMEAU, a collection of French subject headings used by the Bibliothèque Nationale de France and other institutions.

SKOS can be used for subject headings but also many other approaches to organizing knowledge. Because different communities are comfortable with different organization schemes, SKOS is designed to port diverse knowledge organization systems to the Web.

"Active participation from the library and information science community in the development of SKOS over the past seven years has been key to ensuring that SKOS meets a variety of needs," said Thomas Baker, co-chair of the Semantic Web Deployment Working Group, which published SKOS. "One goal in creating SKOS was to provide new uses for well-established knowledge organization systems by providing a bridge to the linked data cloud."

SKOS is part of the Semantic Web technology stack. Like the Web Ontology Language (OWL), SKOS can be used to define vocabularies. But the two technologies were designed to meet different needs. SKOS is a simple language with just a few features, tuned for sharing and linking knowledge organization systems such as thesauri and classification schemes. OWL offers a general and powerful framework for knowledge representation, where additional "rigor" can afford additional benefits (for instance, business rule processing).

To get started with SKOS, see the SKOS Primer.

About the World Wide Web Consortium (W3C)

The World Wide Web Consortium (W3C) is an international consortium where Member organizations, a full-time staff, and the public work together to develop Web standards and guidelines designed to ensure long-term growth for the Web. Over 400 organizations are Members of the Consortium. W3C is jointly run by the MIT Computer Science and Artificial Intelligence Laboratory (MIT CSAIL) in the USA, the European Research Consortium for Informatics and Mathematics (ERCIM) headquartered in France and Keio University in Japan, and has seventeen outreach offices worldwide. For more information see


Contact --
Ian Jacobs, <>, +1.718.260.9447

Testimonials for SKOS Recommendation

Computas AS

Computas AS has already delivered commercial projects based on SKOS. Without being a member of the Working Group, the early work we saw instilled great confidence in the process. With the promotion of SKOS to a Recommendation, it has delivered on its promise. Computas AS has also performed an evaluation of SKOS vs. another W3C technology, OWL (which has also been used in commercial projects), and found that there are many cases where SKOS is the right tool for the job and indeed a great one too.

— Kjetil Kjernsmo, Senior Knowledge Engineer, Computas AS

Library of Congress

The Library of Congress welcomes the Simple Knowledge Organization System (SKOS) reaching W3C recommendation status. We expect SKOS to play a role in helping the Library express and relate terms and concepts within its controlled vocabularies, authorities, classification schemes, and thesauri in a Web-ready, interoperable manner. Via our SKOS-based implementation of the _Library of Congress Subject Headings_ within the Authorities & Vocabularies service at, we have demonstrated that implementing SKOS can pay dividends in both current and future metadata services within libraries. Reaching W3C recommendation status cements SKOS as a valuable and viable standard.

— Sally H. McCallum, Chief, Network Development and MARC Standards Office, Library of Congress

W3C Health Care and Life Sciences Interest Group

In the Terminology task force of the Semantic Web Health Care and Life Sciences Interest Group (HCLSIG), we are actively involved in the representation of existing biomedical vocabularies, such as SNOMED and the Gene Ontology, in SKOS so that their concepts can be integrated into our applications. Putting these vocabularies into a Semantic Web context has generally meant producing an OWL representation. Despite the power of OWL, the task of community scale agreement on even basic axiomatic OWL definitions as a primary knowledge resource requires deep and widespread understanding of OWL semantics to succeed. SKOS provides a new level of knowledge representation at the lexical level rather than the semantic, where community agreement on terms and the relationships between concepts is already in the grasp of expert communities. We feel that there will be a shift to SKOS as the de- facto standard for representing biomedical terminologies because of the standard way of describing components of vocabularies that it provides.

— Andrew Gibson, M. Scott Marshall (University of Amsterdam), John Madden (Duke University) for W3C Semantic Web Health Care and Life Sciences Interest Group (HCLSIG)

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