6.5. Definition: Are Use Cases Functional Requirements?
Use cases are requirements, primarily functional or behavioral requirements that indicate what the system will do. In terms of the FURPS+ requirements types, they emphasize the "F" (functional or behavioral), but can also be used for other types, especially when those other types strongly relate to a use case. In the UPand many modern methodsuse cases are the central mechanism that is recommended for their discovery and definition.56 A related viewpoint is that a use case defines a contract of how a system will behave [Cockburn01].To be clear: Use cases are indeed requirements (although not all requirements). Some think of requirements only as "the system shall do…" function or feature lists. Not so, and a key idea of use cases is to (usually) reduce the importance or use of detailed old-style feature lists and rather write use cases for the functional requirements. More on this point in a later section.