Is TIME an actor in a use case?

Question

Alright, on a true false question:

a)The actors of a system are only represented by humans or another software components.

I said TRUE, and the teacher marked it as wrong, not because he considered that I missed hardware components (which I guess I would partially concede), but because, on his words:

"TIME is also an actor."

How would an use case diagram consider TIME as an actor??

Please refer to any bibliography which considers time an actor. I haven't found any, and truthfully I don't think it makes any sense. Time doesn't act by itself, it's either a system or a person that works on a schedule.

Answer 1

An actor can be considered as someone or something that starts a use case. Scheduled tasks are started by "time". In this sense, "time" is an actor, because it starts a use case.

Example:

A report must be generated each 6 hours. So, the time "6 hours" must be an actor because the generate task will be started each 6 hours.

Answer 2

Time interacts with the system. E.g. time goes past and the system must do something based on that "action".

Answer 3

The UML 2 Use Case Diagramming Guidelines here...

http://www.agilemodeling.com/style/useCaseDiagram.htm

... show how Time can be represented.

I suspect though that you should ask your Teacher to explain how Time is an actor and how it's represented on a Use Case diagram because, after all, they'll be marking your next assignment and so their interpretation trumps all others :-)

Oh, and Wikipedia says Time is an Actor, so it must be true:

http://en.wikipedia.org/wiki/Use_case

Answer 4

I agree with having Time as an actor. If a use case in the system is triggered at a certain moment of time I'd model Time as actor and relate it with that use case. Time can be considered an external entity (and thus an actor) in these scenarios

Answer 5

This question is quite old now. But have a look at

Gathering Additional Requirements via Temporal Actors by Moncef Bari, Ghislain Lévesque and Ahmed Seffah