USE Cases

A USE Case is a narrative document that describes the sequence of events of an actor (an external agent) using a system to complete a process. Use cases capture who (actor) does what (interaction) with the system, for what purpose (goal), without dealing with system internals. A complete set of use cases specifies all the different ways to use the system, and therefore defines all behavior required of the system, bounding the scope of the system.

• Use cases are stories, scenarios, or descriptions of using a system. Use cases are not exactly like requirements or functional specs, but they illustrate and imply requirements in the stories they tell.

• Use cases can be developed as an aid to producing requirements; they can also be developed from the requirements as a direct aid in system design.

• Use cases are used as input to CRC card sessions.

• UML has notation to express use cases... we will do it informally.

• One of the big dangers of use-cases is that of structuring the software to mimic the use cases. Use-cases provide an external view of the system; the software is often structured in a completely different way. The biggest danger is that of turning each use-case into a procedural controller which acts upon simple data holders. When using use-cases remember that they are an external view only.

Examples for voting system

caveat emptor... they may not be the best one can do

Resources

• use case template

• another definition

• Functional requirements and Use Cases

• Use Case Zone

• UseCases.org