Simple Knowledge Organization System has become the latest Semantic Web standard.

The World Wide Web Consortium announced today (August 18) that SKOS is now a recommendation.

According to the reference document that defines it, SKOS is a “a common data model for sharing and linking knowledge organization systems via the Web”.

The W3C’s SKOS primer elaborates:

The Simple Knowledge Organization System (SKOS) is an RDF vocabulary for representing semi-formal knowledge organization systems (KOSs), such as thesauri, taxonomies, classification schemes and subject heading lists. Because SKOS is based on the Resource Description Framework (RDF) [RDF-PRIMER] these representations are machine-readable and can be exchanged between software applications and published on the World Wide Web.

SKOS has been designed to provide a low-cost migration path for porting existing organization systems to the Semantic Web. SKOS also provides a lightweight, intuitive conceptual modeling language for developing and sharing new KOSs. It can be used on its own, or in combination with more-formal languages such as the Web Ontology Language (OWL) [OWL]. SKOS can also be seen as a bridging technology, providing the missing link between the rigorous logical formalism of ontology languages such as OWL and the chaotic, informal and weakly-structured world of Web-based collaboration tools, as exemplified by social tagging applications.

The aim of SKOS is not to replace original conceptual vocabularies in their initial context of use, but to allow them to be ported to a shared space, based on a simplified model, enabling wider re-use and better interoperability.

In other words, it’s complicated. But it’s obviously a technology that’s key to building the Semantic Web.

According to today’s W3C press release, the U.S. Library of Congress has published its subject headings—which are used to categorize books, videos, and other resources—in SKOS.

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