A terminological default logic (Preliminary Draft)

{\em Terminological Logics\/} are knowledge representationformalisms of considerable applicative interest, as they arespecifically oriented to the vast class of application domains that aredescribable by means of taxonomic organizations of complex objects.Although the field of terminological logics has lately been an activearea of investigation, few researchers (if any) have addressed theproblem of extending these logics with the ability to perform {\emdefault reasoning}. Such extensions would prove of paramountapplicative value, as for many application domains a formalization bymeans of monotonic terminological logics may be accomplished only atthe price of oversimplification. In this paper we show how we caneffectively integrate terminological reasoning and default reasoning,yielding a {\em terminological default logic}. The kind of defaultreasoning we embed in our terminological logic is reminiscent ofReiter's Default Logic, but overcomes some of its drawbacks bysubscribing to the ``implicit" handling of exceptions typical of theMultiple Inheritance Networks with Exceptions proposed by Touretzky andothers.