<P> A 2006 survey of ontologies available on the web collected 688 OWL ontologies . Of these, 199 were OWL Lite, 149 were OWL DL and 337 OWL Full (by syntax). They found that 19 ontologies had in excess of 2,000 classes, and that 6 had more than 10,000 . The same survey collected 587 RDFS vocabularies . </P> <P> An ontology is an explicit specification of a conceptualization . </P> <P> The data described by an ontology in the OWL family is interpreted as a set of "individuals" and a set of "property assertions" which relate these individuals to each other . An ontology consists of a set of axioms which place constraints on sets of individuals (called "classes") and the types of relationships permitted between them . These axioms provide semantics by allowing systems to infer additional information based on the data explicitly provided . A full introduction to the expressive power of the OWL is provided in the W3C's OWL Guide . </P> <P> OWL ontologies can import other ontologies, adding information from the imported ontology to the current ontology . </P>

Owl 2 web ontology language structural specification and functional-style syntax