event

An event is a 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 systesm, but are sensed by it, for example by a camera for the lightening strike or electrcla swithc 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 soenthing virtually instantaneous. Often at a closer analyss 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, then perhaps waits in a mesage queue, etc. However, it is often useful to ignore these details and think simply of a momentary event giving rise to resulting {[action}}.