Triggers are dynamically created and destroyed on an application database. Rules are represented in active databases as ECA (event-condition-action) items, in which an action formulates a reaction to an event and is executed after the rule is triggered when the condition is evaluated to true. The event is defined as an instantaneous and atomic (that is, the event either happens completely, or not at all) point of occurrence within an application. Events can be classified as either database, temporal, or user-defined events, and their type can be either primitive or composite.