Final answer:
An actor in system modeling is a role played by a user or a system that interacts with the subject. An actor can be non-human, such as a system or device, and generalization is applicable to actors.
Step-by-step explanation:
The question focuses on the concept of an Actor within the context of modeling, particularly in systems and software engineering. An Actor is used in use-case modeling to specify a role played by a user or any other system that interacts with the subject.
Let's examine the given options:
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- A. An actor does not always need to be human. It can also be an external system or a device that interacts with the system.
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- B. A subsystem or external system can indeed be modeled as an actor. This is because an actor can be anything that exchanges information with the system being modeled.
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- C. An actor is indeed a role a user plays with respect to the system, which represents its interactions with the system.
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- D. Generalization is applicable to actors. This means that an actor can inherit the role and characteristics of another actor.
Therefore, the correct cases for an actor are C, and the statements in A, B, and D are not true. An actor can be a human, a system, or a device, and generalization can be used to represent actors in a use-case diagram.