Association direction in use case diagrams

Question

What is the meaning of the direction of an association between actor and use case in a UML use case diagram? Is it data flow direction or control flow direction? Does the standard say anything about this?

Answer 1

Ah no. This is an association, in the norm, association between actor and use has no direction. Please see image extracted from the norm.

The usage is: if the actor is on the left, it means that's a "primary actor", the actor who activates the use case. If the actor is on the right, it means that the actor is a secondary one: he participates to use case but does not activate it.

Please, take care to the multiplicity: "The example shows that a Customer or Administrator may or may not participate in any of their associated UseCases (hence the 0..1 multiplicity). From the UseCase perspective, every UseCase in the example must have an Actor to initiate it (hence the 1 multiplicity). The Deposit and Register ATM UseCases require participation by the Bank, while the bank can participate with many Deposit and Register ATM UseCases at the same time." (extract, p641)

The point is if you get a lot of actors, keeping them on the left or the right is not easy. So "I" (but this is my way, not the norm) use directed association, if this is from the actor to the use case, it means that's the actor is a primary one, if this is from the use case to the actor it means this is a secondary one.