Abstract
Description logics are formalisms designed for a logical reconstruction of representation tools such as frames, object oriented and semantic data models, semantic networks, type systems, and feature logics. Nowadays, description logics are also considered the most important unifying formalism for the many object centred representation languages used in areas other than knowledge representation. Important characteristics of description logics are high expressivity, together with decidability, which guarantee that reasoning algorithms always terminate with the correct answers. The article introduces temporal extensions of description logics, through the detailed analysis of a case study, involving the combination of a rather expressive description logic with the basic tense modal logic over a linear, unbounded, and discrete temporal structure. ALCQIT is the temporal description logic considered as the case study. This language is obtained by combining a standard tense logic and the non temporal description logic ALCQI with axioms. We first introduce the non temporal part of the language, and then we present its combination with the tense logic. Finally, we briefly report on how other approaches in extending description logics with time relate to the case study.