Use case

In software and systems engineering, the phrase use case is a polyseme with two senses:

1. A usage scenario for a piece of software; often used in the plural to suggest situations where a piece of software may be useful.
2. A potential scenario in which a system receives an external request (such as user input) and responds to it.

This article discusses the latter sense. (For more on the other sense, see for example user persona.)

A use case is a list of actions or event steps typically defining the interactions between a role (known in the Unified Modeling Language (UML) as an actor) and a system to achieve a goal. The actor can be a human or another external system. In systems engineering, use cases are used at a higher level than within software engineering, often representing missions or stakeholder goals. The detailed requirements may then be captured in the Systems Modeling Language (SysML) or as contractual statements.