event

An event is an incident or change that happens at a particualr moment, for example, a lightening strike or person pressing a key. In computer systems, some events may originate outside the system but are sensed by it; for example by a camera for the lightening strike or electrcal swithch for the keypress. Other events may be raised internally, for example, when one agent sends a message to another.

When we use the term 'event', we often envisage it as being something virtually instantaneous. Often at a closer analysis events take time: the user's finger gradually moves the key downwards until it makes first partial and then complete electrical contact, then this is sensed, electrical signals go down wires into the compter, this is perhaps recorded in a mesage queue, where it waits, etc. However, it is often useful to ignore these details and think simply of a momentary event giving rise to a resulting action.