SEMANTICS OF INHERITANCE IN LOGICAL OBJECT SPECIFICATIONS

Our goal is to integrate the paradigms of object-oriented structuring and of rule-based specifications for databases. In this paper, we consider hierarchical specifications of objects and object types with attributes defined 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 defining formulas are interpreted like defaults of different priorities corresponding to levels in the object type hierarchy. Here, minimal model semantics known from default reasoning in artificial intelligence or from database completions can be utilized, but must be modified to respect object-oriented issues, in particular locality. We prove that intended models exist for object and composite specifications under natural conditions, even if general clauses are used as defaults.