TriGS: Making a Passive Object-Oriented Database System Active

Active object-oriented concepts are especially useful in the area of nonstandard applications in order to express an event-driven and constraint-driven system environment. Several attempts have been made to integrate active concepts into object-oriented databases. Current approaches to active object-oriented database systems, however, do not consider the various active concepts together with some of the basic object-oriented concepts; they do not exploit all the advantages of object-oriented features to make the whole system more expressive and open for changing requirements. The system TriGS (=Trigger system for GemStone) fills this gap. TriGS makes explicit use of objects, message passing, inheritance, overriding and overloading to provide a seamless integration between triggers and an object-oriented data model. Triggers consisting of events, conditions, and actions monitor the behavior of objects and can be attached to specific classes or defined independently of any class hierarchy. Since triggers are activated at different levels of granularity ranging from the object instance level to the object class level, a powerful exception handling mechanism is also supported. Moreover, triggers can be dynamically defined, modified, and extended independently of any application. TriGS is implemented on top of the object-oriented database system GemStone ™ as part of a larger EC ESPRIT project aiming at the development of next-generation production scheduling and control systems.