What is an actor?

• A. A person
• B. An external system
• C. A person or external system that interfaces with your system
• D. A data structure

Answer: (C)

In system modeling, an actor is any external entity that interacts with the system to achieve a goal. It isn’t limited to people; it can be a person or another system or external service that communicates with your system through inputs or messages. This is why the best answer is the one that says a person or external system that interfaces with your system.

The other ideas are too narrow: a person is only part of what an actor can be, and an external system is only part of what an actor can be. A data structure is an internal component, not an external entity that interfaces with the system.