Unified Modeling Language Reference Manual, The, Second Edition

use case

The specification of sequences of actions, including variant sequences and error sequences, that a system, subsystem, or class can perform by interacting with outside objects to provide a service of value.

See also actor, classifier, subject.

Semantics

A use case is a coherent unit of functionality provided by a classifier (a system, subsystem, or class) as manifested by sequences of messages exchanged among the system and one or more outside users (represented as actors), together with actions performed by the system.

The purpose of a use case is to define a piece of behavior of a classifier (including a subsystem or the entire system), without revealing the internal structure of the classifier. The classifier whose behavior is described ...