Events with Attributes in an Active Database

In an active database, triggers are red in response to the occurrence of events. Events may have attributes, and the values of these attributes may be used as parameters to functions invoked in the action part. Composite events may be speciied as the composition of primitive events in the database system. The attributes of a composite event are derived from the attributes of its constituent primitive events. Event attributes become even more important when events are composite. These attributes can be used to restrict composite events that are recognized (by relating attributes of constituent primitive events), and to specify database state information from the time of occurrence of a consitutent event that must be preserved, as an attribute, for the composite event. We present a formalism for specifying attributes on composite events using event expressions. We show how such composite events can be detected eeciently by extended nite state machines.