UML Weekend Crash Course™ - To Parent Directory

230
Sunday Morning
Figure 22-4 represents the change events that cause the Order to be archived. In both
cases, the Order is waiting until there has been no activity on the Order for 90 days.
Cancelled
when today >
(last update +90 days)/
setArchived()
Shipped
when today > (last update + 90 days)/
setArchived()
Figure 22-4 Change event “when today > (last update +90 days)”
As a reminder, note that this event is only evaluated while the Order is either Cancelled
or Shipped. The fact that the event is not drawn from the other states to archived means
that the object will not test for that condition while in those states. Remember that what
does not show on a Statechart tells you almost as much as what is shown on the diagram.
Making events conditional
A guard condition controls the response to an event. When an event occurs, the condition is
tested. If the condition tests true, the corresponding transition takes place along with any
and all associated actions; otherwise, the event is ignored.
Figure 22-5 models one of the transitions from the Tentative state to the Placed state.
The triggering event is “receivePmt(amt).” But receiving the payment will not upgrade the
Order to Placed unless it was actually enough to pay for the Order. The net effect of the
event is that the object acknowledges the event, evaluates the effectiveness of the event,
and either accepts or rejects it based on the guard condition. If the event is rejected, the
object remains unchanged.
receivePmt(amt)[amt not < amt_due]/
placeOrder()
Tentative
Placed
On entry/issueConf()
Figure 22-5
Guard condition [amt not