What is the primary function of a use case diagram?

The primary function of a use case diagram is to provide an overview of several use cases within a system, illustrating how users interact with that system. Use case diagrams focus on the relationships between actors (users or other systems) and the use cases (functionalities or services) that the system offers. They help to visualize the functionality that is available to the users, highlighting the goals and what tasks actors want to accomplish.

This visualization is essential as it helps stakeholders, including developers, business analysts, and project managers, to understand the system's requirements at a high level. Furthermore, use case diagrams are widely utilized in the requirements gathering process, ensuring that all necessary interactions are identified and documented before moving onto more detailed design and implementation phases.

While modeling system architecture, outlining user interface designs, and describing programming logic are important aspects of software development, they are not the primary focus of a use case diagram. Instead, they delve into lower levels of detail that move beyond the actor and use case interactions, which is the main focus of use case diagrams.