Drools Fusion is a Drools module that is a part of the Business Logic Integration Platform. It is the Drools event processing engine covering both CEP and ESP (these terms will be used interchangeably in this book). Each event has a type, a time of occurrence, and possibly a duration. Both point-in-time (zero duration) and interval-based events are supported. An event can also contain other data such as any other fact: properties with name and type. All events are facts, but not all facts are events. An event's state should not be changed; however, it should be noted that is valid to populate unpopulated values. Events have clear life cycle windows and may be transparently garbage collected after the life cycle window expires (for example, we may be interested only in transactions that happened in the last 24 hours). Rules can deal with time relationships between events.