States may idle, perform actions or invoke operations, called activities . Actions that do not themselves cause a change in state are called static reactions . These may be performed within states when a trigger is sensed or they may be performed as a state is entered or exited. States are represented graphically as rounded rectangles. Triggers Triggers are the dynamic elements in statecharts.
Triggers cause state transitions or static reactions.
Events, conditions or a combination of both can be triggers. Sources for internally generated events are actions, timeouts or sensors for detecting the status of states, activities, conditions and data items. Events may also be a compound set of other events and conditions. Events are represented as a alphanumeric labels on transition lines or in the On field in state definitions. Conditions can be edge or level-sensitive.