UML Weekend Crash Course™ - To Parent Directory

78
Saturday Morning
Table 7-7
The Fill Order Use Case Narrative: Post-conditions
Field Name
Post-conditions
Cancel:
Field Description
Normal termination:
The changes to the Order must be saved
(The backorder is handled by the CreateBackorder Use Case)
The Order must be saved unchanged
If a backorder was being created, it must be cancelled
Note that the post-conditions include some items that go a bit beyond the scope of a Use
Case, like saving the Order. A rule of thumb with Use Cases is that you include only what
the user can see, and what can be inferred by what they can see. In this case, if the user
gets a message indicating that the Order was updated, then you would include the messages
in the Use Case dialog. You would not include the actual steps for updating the Order in the
database. If your team feels that information is really needed, first make certain that users
agree that your understanding, as documented in the narrative, was correct. Then you could
take the Use Case description down a level to address the requirements you know have to be
supported by the design. This rule is a little bit gray, but it comes with the territory.
REVIEW
The Use Case narrative describes, in user-level terms, what the users expect from the Use
Case. The Use Case is a feature of the system with a beginning, a middle, and an end. As
such, it needs to be explained in terms plain enough for the users to understand and verify,
but precise enough for analysts and designers to rely on in order to build the system.
The features of a Use Case narrative aren’t standardized, but this session provides a set of
common elements in wide use:
Use Case initiation describes how to start a Use Case.
Assumptions define conditions that must be true, but are not tested in this Use
Case.
Pre-conditions define conditions that must be true, and are tested in this Use Case.
The Use Case dialog explains how the user (whether an actor or another Use Case)
interacts with the system during the execution of the Use Case.
Use Case terminations define the different mechanisms that can cause the Use Case
to stop execution.
Post-conditions define the state of the system that must be true when the Use Case
ends. This helps prevent Use Cases from leaving the system in an unstable condition
for other Use Cases that follow.