An on statement specifies an event expression and a listener action. When the correlator executes an on statement it creates an event listener. An event listener observes each event processed by the correlator until an event or a pattern of events matches the pattern specified in the event listener’s event expression. When this happens the event listener triggers, causing the correlator to execute the listener action. At this point, depending on the form of the event expression, the event listener either terminates or continues listening for additional matching event patterns.

An event listener analyzes the event stream until one of the following happens:

The correlator can support large numbers of concurrent event listeners each watching for an individual pattern.