Beyond Coupling Modes: Implementing Active Concepts on Top of a Commercial ooDBMS

Active object-oriented database systems are especially useful in the area of nonstandard applications in order to implement an event-driven and constraint-driven system environment. Several approaches exist in literature integrating active concepts into object-oriented databases. For most systems, their knowledge model is based on Event/Condition/Action rules, and their execution model is based on coupling modes, specifying the temporal relationships between rule triggering and condition evaluation, and between condition evaluation and action execution, respectively. The expressive power of coupling modes, however, is insufficient for specifying certain execution semantics required by nonstandard applications. The system TriGS (=Trigger system for GemStone™) fills this gap. Instead of exploiting coupling modes TriGS uses an event specification mechanism not only for defining the points in time for rule triggering but also the points in time for condition evaluation and action execution. A first prototype of TriGS implemented in Smalltalk and GemStone on SUN™ workstations is operational.

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