Semantics of Inheritance in Logical Object Speciications

Our goal is to integrate the paradigms of object-oriented structuring and of rule-based speciications for databases. In this paper, we consider hierarchical spec-iications of objects and object types with attributes deened by logical rules, and we explain their local (single object) semantics as well as their composite (object society) semantics. In order to allow inheritance with exceptions (overriding) even for rules, the deening formulas are interpreted like defaults of diierent priorities corresponding to levels in the object type hierarchy. Here, minimal model semantics known from default reasoning in artiicial intelligence or from database completions can be utilized, but must be modiied to respect object-oriented issues, in particular locality. We prove that intended models exist for object and composite speciications under natural conditions, even if general clauses are used as defaults.