A UML use-case diagram shows the relationships among actors and use cases within a system. They are often used to

1. ■ provide an overview of all or part of the usage requirements for a system or organization in the form of an essential model (Constantine and Lockwood 1999, Ambler 2004) or a business model (Rational Corporation 2002);

2. ■ communicate the scope of a development project;

3. ■ model the analysis of usage requirements in the form of a system use-case model (Cockburn 2001).

A use-case model comprises one or more use-case diagrams and any supporting documentation such as use-case specifications and actor definitions. Within most use-case models, the use-case specifications tend to be the primary artifact, with UML use-case diagrams filling a supporting role as the “glue” that keeps your requirements model together. Use-case models should be developed from the point of view of your project stakeholders and not from the (often technical) point of view of developers.

Use-Case Guidelines

A use case describes a sequence of actions that provide a measurable value to an actor. A use case is drawn as a horizontal ellipse on a UML use case diagram, as you can see in Figure 14.

Begin Use-Case Names with a Strong Verb

Good use-case names include Withdraw Funds, Register Student in Seminar, and Deliver Shipment because it is clear what each use case does. Use-case names beginning with weak verbs such as “process,” “perform,” and “do” are often problematic.