Manufacturing work cell - Software Development Case Studies in Java - page 207

DiscreteProcess DiscreteClock

0 .. n 1 .. 1

activeEvent
notifyEvent

scheduleEvent

1 .. 1

0 .. n

PieceSource DicreteEvent

name
raiseTime

subscription

Figure 9.7 The analysis diagram of the first prototype

DiscreteEvent is the basic entity that records the name of an event (e.g.
WORKDONE ) and its raise time. DiscreteProcess represents the generic finite
state automaton and has two main functionalities:

To update the automaton current state when an enabled event is notified.

■

To activate events when a state transition occurs.

■

DiscreteClock represents the centralized clock and has two main function-
alities:

To schedule events. It is the bookkeeper of the current time and of the
scheduled events. It knows what event is next to be raised and when. It
also knows which processes are listening to which event.

■

To raise events when their lifetime has expired. It notifies the processes
that are listening to them.

■

PieceSource represents the automated inventory system that feeds the drill
and cutter input buffers with raw pieces. It generates LOADED events at
random time instants.
The resulting application has a graphical user interface that displays the
sequence of events that are fired from the beginning to the end of the simu-
lation. For each event, the interface shows the event name, the raise time
and the name of the process that is broadcasting the event.

9.4.2 Design

We need the class WorkCell to represent the entire manufacturing work cell.
It encapsulates the discrete processes embedding the dynamics of the work
cell subsystems (see Figure 9.8). This class listens to all the events raised by
the work cell subsystems and manages the graphical user interface that
displays the state of the sequential processes every time a state transition
occurs. WorkCell encapsulates the global clock that synchronizes the event-
based communication between the discrete processes.