29.1. Events, States, and Transitions

An event is a significant or noteworthy occurrence. For example:

• A telephone receiver is taken off the hook.

A state is the condition of an object at a moment in time—the time between events. For example:

• A telephone is in the state of being “idle” after the receiver is placed on the hook and until it is taken off the hook.

A transition is a relationship between two states that indicates that when an event occurs, the object moves from the prior state to the subsequent state. For example:

• When the event “off hook” occurs, transition the telephone from the “idle” to “active” state.