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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.
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In a use-case diagram, users of the system are depicted as actors. Each actor performs a specific role in the system, which is called a use-case. More than one actor can perform a single use-case. An actor can be a person, such as a customer, or a computer, such as a database system or server.
Actors. A use case diagram shows the interaction between the system and entities external to the system. These external entities are referred to as actors. Actors represent roles which may include human users, external hardware or other systems.
System is never an actor in a use case model. You have to think about the thing that is triggering the system under investigation to carry out a process. The system itself is dumb and cannot trigger itself into action. It can only be triggered by a user or by Time.
Every use case contains three essential elements: The actor. The system user -- this can be a single person or a group of people interacting with the process. The goal.
I don't agree that time is an actor. What you have to really think is who is going to benefit from the action and put in the functional description setting the timetable creation and execution. Take a look at this article:
Dr. Use Case
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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.
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