Timer and Counter Triggers in RAPID

Triggers are event-condition-action rules in active databases. In order to improve the power of expression of triggers, the event part is typically modeled as a composite event or an event expression. We propose to model events as finite state automata of pre-defined types. We show how two example triggers types may be defined using a trigger definition language based on SQL3. The timer trigger is a trigger based on the timer automaton, and the counter trigger is based on the counter automaton. The approach results in a intuitive and simple triggers definition syntax and it allows for a stepwise trigger system implementation in object-oriented environments. The discussed triggers were implemented in the RAPID system‐a temporal and active fast-response database system for industrial applications.