A use case is a sequence of actions that provide a measurable value to an actor. Another way to look at it is a use case describes a way in which a real-world actor interacts with the system. In a system use case you include high-level implementation decisions. System use cases can be written in both an informal manner and a formal manner. Techniques for identifying use cases are discussed as well as how to remain agile when writing use cases.

Informal System Use Cases

Introduction to System Use Cases