SKOSs

SKOS, or Simple Knowledge Organization System, is a W3C standard for representing knowledge organization systems in the Semantic Web. SKOSs are SKOS-based vocabularies and concept schemes that organize concepts such as terms in a thesaurus, a classification, or a taxonomy in a machine-readable form while preserving human-readable labels. The core model defines skos:Concept, skos:ConceptScheme, and skos:Collection, plus properties for labeling and relationships. Concepts may have preferred labels (skos:prefLabel), alternative labels (skos:altLabel), and hidden labels (skos:hiddenLabel). They can be related through broader and narrower links (skos:broader, skos:narrower) and through related (skos:related). Concept schemes group related concepts and can carry metadata.

SKOS supports mapping between concepts in different schemes via properties such as skos:exactMatch, skos:closeMatch, skos:broadMatch, skos:narrowMatch, and skos:relatedMatch, enabling interoperability and cross-walks. Extensions like SKOS-XL allow richer labeling by treating labels as first-class resources with additional properties. SKOS is designed to be lightweight and compatible with RDF and Linked Data, and is commonly serialized in RDF/XML, Turtle, or JSON-LD. While SKOS provides a practical framework for publishing and interchanging knowledge organization structures, it is often used alongside more expressive formalisms such as OWL for advanced reasoning tasks.