In active databases, an implicit event is an event that is implied by an ECA rule definition.
ECA rules were developed as an optimization of condition action rules. The performance of rule evaluation was improved by allowing, or even requiring, explicit definition of when rules should be triggered in the form of events. However, it turns out that it is possible to derive events from the condition in a meaningful way in some cases, and, thus, there are events that can be implied by the ECA rule definition. For example, if the condition is a logical expression A = 5 ∧ B = 3, then a disjunction of the events representing update to the variables can trigger the rule. That is, with implicit events (IFA = 5 ∧ B = 3 DO action) is equivalent to (ONupdateAorupdateBIFA = 5 ∧ B = 3 DO action) with explicit events.