Defeasible Reasoning with Prototype Descriptions: First Steps

The representation of defeasible information in Description Logics is a well-known issue and many formal approaches have been proposed, mostly emerging from existing formalisms in non-monotonic logic. However, in these proposals, little attention has been devoted to studying their capabilities in capturing the interpretation of typicality and exceptions from an ontological and cognitive point of view. In this regard, we are currently studying defeasible reasoning as discussed in the linguistic and cognitive literature in order to understand the important desiderata of defeasibility in commonsense reasoning. In this paper, we provide an initial formalisation of a defeasible semantics for description logics which aims at fulfilling such desiderata. The proposal is based on combining ideas from prototype theory, weighted description logic (aka ‘tooth logic’), and earlier work on justifiable exceptions. The introduced weighted prototypes are normalised with respect to a given knowledge base, which in turn is used to compute a typicality score with respect to an individual. This machinery is then used to determine exceptions in case of conflicting axioms.