A terminological default logic

Terminological Logics are knowledge representation formalisms of enormous applicative interest, as they are specifically oriented to the vast class of application domains that are describable by means of taxonomic organizations of complex objects. Although the field of terminological logics has lately been an active area of investigation, few researchers (if any) have addressed the problem of extending these logics with the ability to perform default reasoning, an important form of non-monotonic reasoning. Such extensions would prove of paramount applicative value, as for many application domains a monotonic formalization may be accomplished only at the price of oversimplification. In this paper we show how we can effectively integrate terminological reasoning and default reasoning, yielding a terminological default logic. The kind of default reasoning we embed in our terminological logic is based on Reiter's Default Logic, but overcomes some of its drawbacks by subscribing to the implicit handling of exceptions typical of Touretzky's Multiple Inheritance Hierarchies with Exceptions.