UML Weekend Crash Course™ - To Parent Directory

Session 16—Modeling the Dynamic View: The Sequence Diagram 169
Bill : Customer
Bill's Order : Order
: Inventory
1: Order()
2: return order
3 [for each product] : additem(product)
4: productAvailable(product)
5: return yes
6 [product available=yes] : addProduct(product)
7: return done
8: return done
There is more to this scenario
than shown here.
Figure 16-1
A basic Sequence diagram
Defining the basic notation of the Sequence diagram
All Sequence diagrams are modeled at the object level rather than the class level to allow for
scenarios that use more than one instance of the same class and to work at the level of
facts, test data, and examples. The Sequence diagram uses three fundamental notation elements:
objects, messages/stimuli, and object lifeline.
In the Sequence diagram, the objects use the same notation as in the Object diagram. In
Figure 16-1, you see the three participating objects lined up across the top of the diagram.
The object lifeline (identified by reference #1 in Figure 16-2) is a vertical dashed line below
each object. The object lifeline always runs from the beginning at the top to the end at the
bottom. The amount of time represented depends on the scenario or other behavior you’re
modeling.