@INPROCEEDINGS{BrandtKuestersetal-KR-2002, author = {S.~Brandt and R.~K{\"u}sters and A.-Y.~Turhan}, title = {{Approximation and Difference in Description Logics}}, booktitle = {Proceedings of the Eight International Conference on Knowledge Representation and Reasoning (KR2002)}, year = 2002, pages = {203--214}, editor = {D.~Fensel and F.~Guinchiglia and D.~McGuiness and M.~A.~Williams}, publisher = {Morgan Kaufmann Publishers}, abstract = {Approximation is a new inference service in Description Logics first mentioned by Baader, Kuesters, and Molitor. Approximating a concept, defined in one Description Logic, means to translate this concept to another concept, defined in a second typically less expressive Description Logic, such that both concepts are as closely related as possible with respect to subsumption. The present paper provides the first in-depth investigation of this inference task. We prove that approximations from the Description Logic ALC to ALE always exist and propose an algorithm computing them. As a measure for the accuracy of the approximation, we introduce a syntax-oriented difference operator, which yields a concept that contains all aspects of the approximated concept that are not present in the approximation. It is also argued that a purely semantical difference operator, as introduced by Teege, is less suited for this purpose. Finally, for the logics under consideration, we propose an algorithm computing the difference.} }