Use cases

While actors provide a starting point for capturing the functional requirements of an information system, use cases deals with the bulk of the details of the functional requirements of an information system.

A use case is a complete interaction of at least one actor and the information system that provides value to at least one participating actor. Let us try to explain this rather long and vague description.

``Complete'' means the interaction cannot only serve as a component of another interaction. This rules ``log in'' out as a possible use case because logging in to a system can only serve as a step of some other uses of an information system. By comparison, ``check grade'' is a complete interaction because an actor can check grade without any further interaction.