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 di#erent 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. 1 Introduction Much has already been said about the relative merits of the object-or...

In this paper we consider supernormal defaults [Poo88] with a strict partial order defining their priorities [Bre91]. We investigate their relation to minimal or preferential entailment and show that the semantics given in [Bre91] has to be modified in order to be equivalent to a preferential model approach. Concering the multiple extension problem, we introduce the careful view as an alternative to the credulous and skeptical one, which is needed to handle the generalized closed world assumption [Min82] within this framework. Given this "declaritive semantics" of such default theories, we will present a deduction algorithm for query answering. Compared to other approaches, the algorithm is quite efficient and general. Especially, it is able to generate disjunctive answers, to support the credulous, skeptical and careful view; and to cut fruitless search paths early. In order to check the applicability of defaults as soon as possible, we introduce the notion of a partial extension. 1 I...

In this paper we present how to extend object specification logic by defaults. Thus overridable rules may be used in specifications which deal not only with object states, but also with dynamic object behaviour like enabling / occurrence of actions and temporal evolution. Defaults are particularly useful to formalize implicit negation, the "minimal change" semantics of actions, inheritance between object classes and aggregation of objects. We demonstrate this by means of examples, and study which default patterns should be used for typical problems of behaviour specification. 1 Introduction In this paper, we consider the different uses defaults may have in specifications of system behaviour. Systems are viewed as societies of interacting objects. To this end, we define a first version of OSD, an object specification logic with defaults, and study typical examples. OSD is based on a temporal logic which allows to refer to the occurrence and enabling of actions in the style of OSL [SSC9...

. This paper aims at integrating techniques of non-monotonic reasoning about updates and of object-oriented specification of information systems. We present how to utilize defaults in specifications of dynamic system behaviour. Thus overridable rules may be used in specifications which deal not only with state structures, but also with state transitions and sequences. Systems are viewed as societies of interacting objects. The underlying object specification logic is based on temporal logic and allows to refer to the enabling and occurrence of actions. It is extended with prioritized defaults and module composition. By discussing a variety of examples, we study which default patterns should be used for typical problems of behavioural specification. 1 Introduction In this paper, we consider the different uses defaults may have in object-oriented specifications of dynamic system behaviour. Systems are viewed as societies of interacting objects. To this end, we define an object specifica...