UML Weekend Crash Course™ - To Parent Directory

Session 17—Applying the Sequence Diagram to the Case Study 181
Begin by identifying all the participating objects. Each object is placed at the top of the
diagram, as in Figure 17-2. The order doesn’t really matter. However, when the diagram is
finished, it sometimes helps to move them around to improve the readability of the messages
on the diagram. This Use Case includes the Order Fulfillment Clerk, the System itself, the
Orders database, two Orders (the primary and the backorder), and the Inventory.
:OrderFulfillment Clerk :System :OrdersDB 12345678:Order 23456789:Order :Inventory
Figure 17-2 Sequence diagram with objects and timelines
The first Sequence diagram models Scenario 1. The first, or primary, scenario should be
the successful path. The success path is almost always the most comprehensive. The other
scenarios are then just deviations from the main scenario.
Each step of the flowchart becomes a message and/or a return on the Sequence diagram
(depending on how the step is described). The first step is “Get Order #.” On the Sequence
diagram (Figure 17-3) this appears as a procedure call (step 1) and a response (step 2).
Note the format of the procedure call (message):
Sequence number (optional)
A colon
Condition (optional)
Operation signature, which is made up of:
Visibility, (+ means public, - private, # protected)
Operation name (getOrderNbr)
Arguments () – no arguments for this call
A colon
Return data type (int – meaning integer value).
:OrderFulfillment Clerk :System :OrdersDB 12345678:Order 23456789:Order :Inventory
1: getOrderNbr():int
2: return 12345678
Figure 17-3
Add steps 1 and 2; get the order number