The owl:Ontology element is a place to collect much of the OWL meta-data for the document. It does not guarantee that the document describes an ontology in the traditional sense. In some communities, ontologies are not about individuals but only the classes and properties that define a domain. When using OWL to describe a collection of instance data the owl:Ontology tag may be needed in order to record version information and to import the definitions that the document depends on. Thus, in OWL the term ontology has been broadened to include instance data.
The rdf:about attribute provides a name or reference for the ontology. Where the value of the attribute is "", the standard case, the name of the ontology is the base URI of the owl:Ontology element. Typically, this is the URI of the document containing the ontology. An exception to this is a context that makes use of xml:base which may set the base URI for an element to something other than the URI of the current document.
<rdfs:comment>An example OWL ontology</rdfs:comment>
The ontology-import construct owl:imports and the
ontology-versioning constructs owl:priorVersion,
owl:backwardCompatibleWith and owl:incompatibleWith are defined in the OWL
vocabulary as instances of the OWL built-in class
owl:OntologyProperty. Instances of
owl:OntologyProperty must have the class
as their domain and range.