Use Case - a sequence of actions that an actor performs within a system to achieve a particular goal. The purpose of this stage is to capture user requirements of the new system using use case diagrams.
Definition: A sequence of actions that an actor performs within a system to achieve a particular goal.
A use case describes one or more courses through a user operation. The basic course must always be present; alternate courses are optional.
Basic course - the main start-to-finish path the user will follow under normal circumstances.
Alternate course - infrequently used path, an exception, or an error condition.
Stated from the perspective of the user as a present-tense verb phrase in an active voice (AdmitPatient, Do Trade Entry, Generate Reports).
Describes one aspect of usage of the system without presuming any specific design or implementation.
Ask "what happens?"
"Then what happens?"
Be relentless.
All required system functionality should be described in the use cases.
Actor - represents a role a user can play with regard to a system.
A user can serve as more than one type of actor.
Use cases appear as ovals, generally in the middle of a use case diagram.
Analysis level and design level use cases.
Should be able to write a solid paragraph or two about a design-level use case.
Use cases should have strong correlations with material in the user manual for the system (write the manual, then write the code). (Write the manual as though the system already exists.)
Use rapid prototyping as frequently as possible.
If you're reengineering an existing legacy system, work from the user manual backward.
A use case captures some user-visible function.
A use case achieves a discrete goal for the user.
A use case may be large or small.
Use cases model a dialogue between an actor and the system.