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)