UML Weekend Crash Course™ - To Parent Directory

Session 22—Modeling the Extended Features of the Statechart 229
Placed
On entry/issueConf()
cancel(datetime)
Cancelled
Figure 22-2
Call event “cancel(datetime)”
Time event
A time event evaluates the passage of time as a trigger. It implies that the object supports
some mechanism to monitor the passage of time. This might be implemented in a number of
ways. The mechanism could be a batch program that runs at intervals to update a time
attribute. The event could use a polling type of implementation where the object constantly
checks to see what time it is.
Use the keyword after to specify the time increment to be evaluated. For example, while
the Order is in the packaged state, it is waiting to be shipped. But if it has not been
shipped within three days, the priority needs to be increased to ensure that it leaves in a
timely manner. Figure 22-3 models an internal event within the packaged state called “after
3 days.” This implies that there will be code within the object that watches the passage of
time to know when to initiate the action “upgrade ShippingPriority().”
Packaged
after 3 days/upgradeShippingPriority()
Figure 22-3
Time event “after 3 days”
Change event
A change event tests for a change in the object or a point in time. Use the keyword when
with the required test. For example, you might need to know when to run a reporting job or
cut invoices so you might say “when 12:00 AM the last day of the month.” Or you might
watch for a specific condition such as a change in temperature. Then you might say, “when
temp > 75 degrees.”