DEGAS : a temporal active data model based on object autonomy

This report defines DEGAS, an advanced active data model that is novel in two ways. The first innovation is object autonomy, an extreme form of distributed control. In comparison to more traditional approaches, autonomous objects also encapsulate rule definitions to make them active. The second innovation of DEGAS is its temporal aspect. Active databases have an inherent temporal element in the specification and detection of event patterns that trigger rules. Autonomous objects, the foundation of the DEGAS data model, are independent processes. Their definition includes their complete behaviour, both potential behaviour in the form of methods and lifecycles and actual behaviour in the form of active rules. Relations between objects are objectified. The specialisation mechanism provided by <font size=-1>DEGAS</font> is a clean addon mechanism well suited to model dynamic evolution of objects in conjunction with relations. In this report we give a full syntactic and semantic definition of the data model. The state of an autonomous object includes its complete history. This allows the active behaviour of the object to be defined in a purely local way.