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)