UML Weekend Crash Course™ - To Parent Directory

Session 23—Applying the Extended Statechart Features to the Case Study 239
Understanding these concepts is a lot easier when you can see an example, so I’m going
to derive a Statechart diagram for the Product object and do it a step at a time so you can
see the progression. I’ll work through the same series of steps for each scenario:
1. Identify the events directed at the lifeline of the Product object.
2. Identify candidate states by isolating the gaps of the lifeline between the incoming
events.
3. Name the candidate states using adjectives that describe the condition of the
object during the period of time represented by the gap.
4. Add the new states and events to the Product Statechart.
The first scenario is modeled in Figure 23-3. There is one incoming event called
Product(PO). This is the constructor operation that creates the object. Before this event,
this particular Product object didn’t exist, so you have discovered the initial state. I’ll name
it “On Order” to show that a record of the Product object is created when the Product is first
ordered.
The self-transition event setPO(PO) does not change the state of the Product. It only
updates a reference that it’s tracking, so I didn’t identify a state change.
:PurchasingClerk :PurchaseOrder :Product
1:PO()
2:PurchaseOrder
3:Product(PO)
does not exist yet
Draft Statechart
Diagram
On Order
4:setPO(PO)
5:Product
6:addProduct(Product)
Initial state
On Order
7:return true
Figure 23-3 Finding the transition events and candidate states for Scenario 1