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61 ).
FIGURE 3-60
Example for an orthogonal state.
stm Weather
Climate
Night
Sunset
Sunrise
terminate
Day
warm cold
coldFront
warmFront
terminate
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3.7.4 Trigger and Event
3.7 The State Machine Diagram
FIGURE 3-61
Example for a transition with behavior.
stm Time of day
Day
Night
terminate
sleep() at(sunset)
getUp() alarmClock on
at(sunset) alarmClock off
Defi nitions
A trigger references exactly one event and establishes a relationship to a
behavior.
An event specifi es some occurrence that can be measured with regard to location
and time.
A trigger is the connecting link between event and behavior in the model. Denoted
at a transition means that the transition is activated as soon as the event occurs.
UML knows four types of events that can trigger a transition ( Figure 3.62 ):
1. A call event occurs when an operation is invoked.
2. A change event occurs when a Boolean expression tests to true. This is the
case when a value has changed accordingly in the system.
3. A signal event occurs when a signal has been received.


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