DEGAS: Capturing Dynamics in Objects

In this paper we introduce Degas (Dynamic Entities Get Autonomous Status), an active temporal data model based on autonomous objects. The active dimension of Degas means that we define the behaviour of objects in terms of production rules. The temporal dimension means that the history of an object is included in the Degas data model. Novel features of Degas axe the encapsulation of the complete behaviour of an object, both potential and actual. Thus, Degas combines dynamic and structural specifications in one model. In addition, Degas allows easy evolution of object capabilities through a clear distinction between inherent types and capabilities that can be acquired and lost. This addon mechanism makes Degas very suitable as a formalism for role modelling. Finally, the rule model in Degas is both simple, through the use of finite automata, and general, because it allows different strategies for dealing with constraints and reacting to events in other objects.