An extension point in the Use Case represents the location at which the extension can be inserted. In the Use Case diagram, the extension point is used together with the extend relationship.
To add an extension point to the Use Case
Draw an extend relationship from the extending Use Case to the extended Use Case.
Subsequent actions depend of whether the extended Use Case has at least one extension point already:
If there are no extension points, the dialog appears asking the confirmation to add a new extension point. Click Yes and type the name of the extension point.
If there is at least one extension point, the Extension Points dialog opens displaying the list of extension points of that Use Case. Click Create, type the name of the new extension point, and click Close.
You can also add extension points via the Specification window of the Use Case. For this, click Extension Points at the left side of the Specification window and type name of the new extension point.