Matching in

Matching of concepts with variables (concept patterns) is a relatively new operation that has been introduced in the context of concept description languages (description logics), originally to help discard unimportant aspects of large concepts appearing in industrial-strength knowledge bases. This paper proposes a new approach to performing matching, based on a \concept-centered" normal form, rather than the more standard \structural subsumption" normal form for concepts. As a result, matching can be performed (in polynomial time) using arbitrary concept patterns of the description language FL : , thus removing restrictions from previous work. The paper also addresses the question of matching problems with additional \side conditions", which were motivated by practical experience.