Use cases model a dialogue between an actor and the system. They represent the functionality provided by the system; that is, what capabilities will be provided to an actor by the system. The collection of use cases for a system constitute all the defined ways the system may be used. The formal definition for a use case is: A use case is a sequence of transactions performed by a system that yields a measurable result of values for a particular actor.
The following questions may be used to help identify the use cases for a system:
What are the tasks of each actor?
Will any actor create, store, change, remove, or read information in the system?
What use case will create, store, change, remove, or read this information?
Will any actor need ...