usecase

A use case is a description of how a system behaves in response to a request from an external actor to achieve a specific goal. Use cases are used to capture functional requirements from the perspective of actors interacting with the system, rather than to specify user interface details.

A use case typically defines a system boundary, the primary actor, one or more secondary actors, and the goals they seek to accomplish. The main or happy-path flow describes the steps leading to successful completion; alternative flows cover variations, errors, or exceptional conditions. Pre-conditions describe the state required before execution, and post-conditions state the result after completion.

Use cases are often written as narratives, sometimes with a structured template listing actors, goals, flows, and nonfunctional considerations. In UML, use-case diagrams visualize the relationships between actors and the use cases they participate in, showing system scope and interactions.

Origin and usage: The concept was popularized by Ivar Jacobson in the 1990s as part of the Object-Oriented Software Engineering methodology. Use cases became a standard element in software requirements and were incorporated into the Unified Modeling Language (UML). They are commonly used to drive requirement validation, test case design, and acceptance criteria.

Relation to other methods: Use cases focus on functional behavior and user goals, while user stories describe smaller, user-centered requirements from a stakeholder perspective. Use cases can be complemented by scenarios, activity diagrams, and sequence diagrams to model flows in more detail.