What is the purpose of a use case within a system's design?

• A. To define system deployment requirements
• B. To describe user-system interactions to achieve a goal
• C. To capture the system's data model
• D. To specify performance benchmarks

Answer: (B)

A use case focuses on the sequence of interactions between a user (actor) and the system to achieve a specific goal. It describes what the user does, how the system responds, and what the resulting outcome should be. This perspective is essential because it captures the functional behavior of the system from the user's viewpoint, helping designers understand and communicate how the system should behave in real scenarios, including alternate or error flows.

That’s why this option is the best: it centers on user goals and the system’s responses to fulfill them, which is exactly what a use case is meant to illustrate. The other concepts relate to different design concerns—deployment details, data structure, or performance targets—which are distinct artifacts and not what a use case aims to describe.