UML Weekend Crash Course™ - To Parent Directory

Session 19—Applying the Collaboration Diagram to the Case Study 197
The next step in the flowchart says that the System tells the OrderFulfillmentClerk to
display the Order it just found in the database. This sounds a bit odd until you realize that
the OrderFulfillmentClerk represents the interface that the Order Fulfillment Clerk will use for
this Use Case. So in reality, the System is telling the screen to display the data. Figure 19-6
adds the asynchronous message and line style arrow alongside sequence #1, going in the
same direction between the same two objects.
:OrderFullfillment Clerk
:OrdersDB
1 : getOrderNbr():int
4 : return 12345678
2 : return 12345678
3 : getOrder(ordernbr.int) : Order
5 : displayOrder(Order): void
:System
Figure 19-6 Modeling the next step in the flowchart: Display the Order
Figure 19-7 shows the completed Collaboration diagram for the first scenario.
In every synchronous message, I chose to show the return as well. Many people
say that you should only show the return if it isn’t obvious. Personally,
Note I believe that strategy leaves a lot of room for mistaken assumptions. I also
firmly believe that the purpose for modeling is to get the information out
where everyone can see it. Using shortcuts hides information.
For the second scenario, insert a comment referring to steps 1 through 4 of Scenario 1,
and then add the new event for Scenario 2. This time the message from the System to the
OrderFulfillmentClerk is an asynchronous event. The System merely sends the message and
goes about its job without waiting for any reply. Figure 19-8 shows the use of the asynchronous
solid line style arrow for the displayMsg(char) message.