  Simple Knowledge Organization System (SKOS) provides a data model and
vocabulary for expressing Knowledge Organization Systems (KOSs) such as
thesauri and classification schemes in Semantic Web applications. This paper
presents the main components of SKOS and their formal expression in Web
Ontology Language (OWL), providing an extensive account of the design decisions
taken by the Semantic Web Deployment (SWD) Working Group of the World Wide Web
Consortium (W3C), which between 2006 and 2009 brought SKOS to the status of W3C
Recommendation. The paper explains key design principles such as "minimal
ontological commitment" and systematically cites the requirements and issues
that influenced the design of SKOS components.
  By reconstructing the discussion around alternative features and design
options and presenting the rationale for design decisions, the paper aims at
providing insight into how SKOS turned out as it did, and why. Assuming that
SKOS, like any other successful technology, may eventually be subject to
revision and improvement, the critical account offered here may help future
editors approach such a task with deeper understanding.
