Use case relationship with actor

Question

如果A是扩展用例（不是基本用例），那么参与者可以直接引用A吗？

Answer 1

YES The user can as said above, but does not indirectly reference/use it, it must be explicitly modeled.

Drive Truck extends Drive Steering Based Vehicle. It make sense that the Actor could reference either.

Answer 2

You can make the case that there are two kinds of use cases:

• Abstract -- not directly experience by an actor, but extensions ("subclasses") are.

• Concrete -- experienced by an actor.

Answer 3

yes; the fact that A extends some other use-case does not 'hide' it from actors