Use Cases
Overview
Use cases are a means for specifying required usages of a system.
Typically, they are used to capture the requirements of a system,
that is, what a system is supposed to do. The key concepts associated
with use cases are actors, use cases, and the subject.
The subject is the system under consideration to which the use cases
apply. The users and any other systems that may interact with the
subject are represented as actors. Actors always model entities that
are outside the system.The required behavior of the subject is
specified by one or more use cases, which are defined according to the
needs of actors.
Strictly speaking, the term "use case" refers to a use case type. An
instance of a use case refers to an occurrence of the emergent behavior
that conforms to the corresponding use case type. Such instances are
often described by interaction specifications.
Use cases, actors, and systems are described using use case diagrams.