The subfield of artificial iNTelligence concerned with designing and using systems for storing knowledge - facts and rules about some subject. A body of formally represeNTed knowledge is based on a conceptualisation - an abstract view of the world that we wish to represeNT. In order to manipulate this knowledge we must specify how the abstract conceptualisation is represeNTed as a concrete data structure. An oNTology is an explicit specification of a conceptualisation. (1994-10-19)