UML: Use Case Diagram (Essentials)

Use cases are a technique for capturing the functional requirements of a system. Use cases work by describing the typical interactions between the users of a system and the system itself, providing a narrative of how a system is used.

A scenario is a sequence of steps describing an interaction between a user and a system

A use case is a set of scenarios tied together by a common user goal.

In use case–speak, the users are referred to as actors. An actor is a role that a user plays with respect to the system. Actors might include customer, customer service rep, sales manager, and product analyst.