Identify and model the Extends stereotype and generalization of use cases
Extends Stereotype and Generalization
Within any given system, there are usually a number of different ways to accomplish a task.
The UML provides two ways to model these variations: the Extends stereotype and generalization.
Extends dependency Stereotype
Some processes include optional behavior or behavior that is used only in specific circumstances. To include the flow of events in the main flow would unduly confuse the use case narrative. For example, some checking accounts can be attached to a line of credit or savings account. If the client attempts to withdraw funds beyond the checking account balance, extra logic is needed to access the funds in the attached
account. You can separate this extra flow of events into its own use case. When it is needed, it can be referenced in the use case narrative.
Generalization works the same in use case modeling as in object modeling. Both actors and use cases may be generalized.
The specialized form of actor or use case inherits all the properties of the base actor or use case. The specialized element may then override or add to the properties of the base definition. Use case diagrams use the same notation as class diagrams to show generalization. Draw a line from the specialized element to the base or generalized element. Place a triangle at the base element end of the line with the apex touching the base element.