Active rules allow the user to specify, that certain actions have to be executed if an event occurs and a condition is fulfilled at this time. Because active rules consists of an Event, a Condition and an Action, they are abbrivated with ECArule.
Events in ConceptBase are insertions and deletions of objects (Tell/Untell) and queries (Ask). The events are detected during the processing of the input frames. For example, if you tell 2 frames at a time, and the first frame contains an event for an ECArule, than the ECArule is executed before the second frame is processed.
A condition is a ConceptBase query. If the result of the query is non-empty, the action block is executed for each value of the result.
The action part of an ECArule in ConceptBase consists of two parts. The first part is a list of actions, which are executed if the query in the condition has a non-empty result. The other part (ELSE) is a list of actions, which are executed if the query in the condition has an empty result. Possible actions are Tell/Untell of objects, evaluation of queries and execution of any PROLOG predicate.