Basic OWL

OWL extends RDF Schema vocabulary descriptions, allowing us to express claims such as...

Nothing can be both a Document and a Person
grandParent and grandChild are inverses
homepage, nasdaqCode and mbox are uniquely identifying properties
A W3CTeamPerson is a Person whose workplaceHomepage is http://www.w3.org/

...as well as the formally specified interactions amongst all these features.