SNOOP - AN EXPRESSIVE EVENT SPECIFICATION LANGUAGE FOR ACTIVE DATABASES

Making a database system active to meet the requirements of a wide ran ge of applications entails developing an expressive event specificatio n language and its implementation. Extant systems support mostly datab ase events and in some cases a few predefined events. This paper discu sses an event specification language (termed Snoop) for active databas es. We define an event, distinguish between events and conditions, cla ssify events into a class hierarchy, identify primitive events, and in troduce a small number of event operators for constructing composite ( or complex) events. Snoop supports temporal, explicit, and composite e vents in addition to the traditional database events. The novel aspect of our work lies not only in supporting a rich set of events and even t expressions, but also in the notion of parameter contexts. Essential ly, parameter contexts augment the semantics of composite events for c omputing their parameters. For concreteness, we present parameter comp utation for the relational model. Finally, we show how a contingency p lan that includes time constraints can be supported without stepping o utside of the framework proposed in this paper.