Timer and Counter Triggers in RAPID 

by Antoni Wolski

Research Report No. J-4
December 1995

VTT Information Technology
P.O. Box 1201, 02044 VTT, Finland

e-mail: wolski@vtt.fi

Abstract

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 systemÐa temporal and active
fast-response database system for industrial applications.