How does a process activate events?
When a state transition is triggered, the process undertakes some activi-
ties that will be completed after a given time period. The end of these
activities corresponds to the notification of a corresponding event. For
example, when the AGV receives a request of mission, a state transition is
triggered that sets the current state to MOVING EMPTY and activates the
ARRIVED event. The lifetime of this event is set equal to the duration of the
The process activates the ARRIVED event by adding it to the clock's list of
scheduled events. Similarly, PieceSource activates a LOADED event to notify
the drill and cutter that a piece has been loaded into their input buffers.
PieceSource listens to its own events. When a LOADED event is notified, a
state transition activates the next LOADED event.
Figure 9.9 shows the object interaction diagram representing the opera-
tions that class PieceSource executes when it is initialized. First it attaches
itself to the LOADED event. Then it activates the first LOADED event that will
be raised after a random time period.
How does the clock notify events?
Figure 9.9 The initialization of the automated inventory system