SKOS

SKOS, or Simple Knowledge Organization System, is a W3C recommendation for representing knowledge organization systems on the Web. It is designed to enable the sharing, linking, and reuse of controlled vocabularies such as thesauri, classification schemes, subject heading lists, and taxonomies.

The core model introduces concepts such as ConceptScheme, Concept, and a set of labeling and relationship properties. Concepts can be members of a concept scheme, identified by URIs, and labeled with preferred, alternate, and hidden labels. Relationships include skos:broader, skos:narrower, and skos:related for intra-scheme structure, as well as inScheme and topConceptOf to locate concepts within schemes.

SKOS defines mapping properties to relate concepts across schemes: skos:exactMatch, skos:closeMatch, skos:broadMatch, skos:narrowMatch, and skos:relatedMatch.

An optional extension, SKOS-XL, allows labels to be resources rather than plain literals, enabling richer labeling with language tags, metadata, or alternative label forms.

SKOS is implemented on top of RDF and is widely used in libraries, data catalogs, and knowledge graphs to describe controlled vocabularies and to facilitate interoperability and Linked Data.

As part of the W3C Semantic Web standards, SKOS promotes reuse and integration of vocabularies across organizations and applications.