The collection of objects, concepts and other entities thAT are assumed to exist in some area of interest and the relATionships thAT hold among them. A conceptualisATion is an abstract, simplified view of the world thAT we wish to represent. For example, we may conceptualise a family as the set of names, sexes and the relATionships of the family members. Choosing a conceptualisATion is the first stage of {knowledge representATion}. Every knowledge base, knowledge-based system, or knowledge-level agent is committed to some conceptualisATion, explicitly or implicitly. (1994-10-19)