What are they?

Formal, explicit descriptions of "domains of discourse"

a document or file that formally defines the relations among terms. The most typical kind ... has a taxonomy and a set of inference rules. The taxonomy defines classes of objects and relations among them. Berners-Lee 2001

What do they contain?

Declarations of, and constraints on:

  • concepts, classes, sets
  • superclass-subclass inheritance hierarchies, taxonomies
  • features, attributes, roles, properties, slots, predicates (including relational)
  • facets, roles, values, objects
  • individuals, instances