The W3C has published a candidate recommendation of SKOS Simple Knowledge Organization System Reference and a new working draft of SKOS Simple Knowledge Organization System Primer. According to the primer:
SKOS — Simple Knowledge Organisation System — provides a model for expressing the basic structure and content of concept schemes such as thesauri, classification schemes, subject heading lists, taxonomies, folksonomies, and other similar types of controlled vocabulary. As an application of the Resource Description Framework (RDF), SKOS allows concepts to be composed and published on the World Wide Web, linked with data on the Web and integrated into other concept schemes.
This document is a user guide for those who would like to represent their concept scheme using SKOS.
In basic SKOS, conceptual resources (concepts) are identified with URIs, labeled with strings in one or more natural languages, documented with various types of note, semantically related to each other in informal hierarchies and association networks, and aggregated into concept schemes.
In advanced SKOS, conceptual resources can be mapped across concept schemes and grouped into labeled or ordered collections. Relationships can be specified between concept labels. Finally, the SKOS vocabulary itself can be extended to suit the needs of particular communities of practice or combined with other modeling vocabularies.
This document is a companion to the SKOS Reference, which gives the normative reference on SKOS.