The alarm is set to be sensitive to changes in local time (indicated
by the clock face in its symbol). In the Show state we can press Down to unset the
alarm and turn off the icon. Assuming we leave the alarm to ring, when it rings it
follows the transition with the small red bell symbol from the Alarm symbol to the
AlarmRang state. From there, without any buttons being pressed, we move directly to
the Show state, turning off the alarm icon on the way. From the Show state, pressing
Mode will exit the application.
9.4.1 Use Scenarios
An important feature of the Watch modeling language is its support for reuse of
models and model elements. This is present at all levels, and across different watch
families, logical watches, and applications. Reuse here means that two or more parts
of a model refer to the same model element. Since this is a reference rather than a copy,
updates to the reused element will instantly and automatically be in effect in all parts
referring to that element. Reusing rather than copying thus reduces the amount of
work needed for maintenance, reduces the risk of corrections only being made to one
FIGURE 9.7 AlarmClock application
208 DIGITAL WRISTWATCH
copy, and makes the amount of data in the models smaller and thus easier to
understand.
At the Family level, the same Logical Watch can be reused in several Watch
Models: for example, the Simple application for viewing and setting the time is used in
both Celestron and Celestra watches.
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