Concept languages based on KL-ONE [Brachman and Schmolze, 1985] are used to represent the taxonomical and conceptual knowledge of a particular problem domain on an abstract logical level. To describe this kind of knowledge, one starts with atomic concepts and roles, and defines new concepts using the operations provided by the language. Concepts can be considered as unary predicates which are interpreted as sets of individuals, and roles as binary predicates which are interpreted as binary relations bdtween individuals. Examples for atomic concepts may be Human and Male, and for roles child. If the logical connective of conjunction "n" is present as a language construct, one may describe the concept Man as "humans who are male", and represent it by the expression Human N Male. Many languages provide quantification over role fillers which allows for example to describe the concept Father by the expression Man N 3child.Human. KL-ONE was first developed for the purpose of natural language processing [Brazhman et al., 1979], and some of the existing systems are still mostly used in this context (see e.g., SB-ONE [Kobsa, 1989]). However, its success in this area has also led to applications in other fields (see e.g., MESON [Edelmann and Owsnicki, 1986] which is used for computer configuration tasks, CLASSIC [Borgida et al., 1989] which is e.g. used in the area of CAD/CAM, or K-REP [Mays et al., 1988] which is used in a financial marketing domain).