CAU_Event - Event

An event is defined through the state transition of one or more object instances. The event defines potential state transitions by means of pre and post condition, i.e. pre and post-states. Events can be defined on the structure or property level as well as on the extent level.

An event is fired when the instance state before modification returns a true precondition and when the state of the instance after the modification returns a true post-condition. Pre and post-conditions can be defined as functions, expressions or any other type of action. When not defining pre and post-condition any modification on the instance is considered as event.

Special events are system events that are signaled by the database system and usually indicate a change in the state of the instance, which cannot be expressed in terms of pre and post-conditions.

Event definitions are stored globally with a unique name that is constructed from the structure name, the extent or property name and the event name. This allows referring to an event from a far linked instance or registering instances for event observation.

When an event is fired it can be handled by an event handler defined in the causality rule, which is a function, expression or other action again.