Explains
how a particular use case is realized
in the design model through collaborating objects.
A designer may describe the design of
one or more scenarios
from a use case.
- Each is called a use case realization.
Use cases suggest the system operations that appear in an SSD.
A
system operation becomes the initiating message
sent to a controller in a domain-layer interaction diagram.
A domain-layer interaction diagram shows how objects interact to perform the work needed to realize a use case.
As discussed earlier, a use case realization
can be designed directly
from the use case text or domain knowledge.
For some complex system operations, an
operation contract
may be written to provide additional analytical detail.
Example
| Operation | enterItem(itemID: ItemID, quantity: integer) |
|---|
| Cross-Reference | Use case: Process Sale |
|---|
| Precondition | A sale is currently in progress |
|---|
| Postcondition | A SalesLineItem instance, sli, has been created |
|---|
Object Design Examples with GRASP Patterns