Cases

A use case is a technique used in software and systems engineering to capture the functional requirements of a system. Use cases describe the interaction between a primary actor—the initiator of the interaction—and the system itself, represented as a sequence of simple steps. more...

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Actors are something or someone which exist outside the system under study, and who (or which) take part in a sequence of activities in a dialogue with the system, to achieve some goal: they may be end users, other systems, or hardware devices. Each use case is a complete series of events, from the point of view of the actor.

According to Bittner and Spence, "Use cases, stated simply, allow description of sequences of events that, taken together, lead to a system doing something useful." Each use case describes how the actor will interact with the system to achieve a specific goal. One or more scenarios may be generated from each use case, corresponding to the detail of each possible way of achieving that goal. Use cases typically avoid technical jargon, preferring instead the language of the end user or domain expert. Use cases are often co-authored by systems analysts and end users. The UML use case diagram can be used to graphically represent an overview of the use cases for a given system.

Within systems engineering, use cases are used at a higher level than within software engineering, often representing missions or stakeholder goals. The detailed requirements may then be captured in SysML requirement diagrams or similar mechanisms.

History

In 1986, Ivar Jacobson, later an important contributor to the Unified Modeling Language (UML) and Rational Unified Process, first codified the visual modeling technique for specifying use cases. Originally he used the terms usage scenarios and usage case, but found that neither of these terms sounded natural in English, and eventually he settled on the term use case. Since Jacobson originated use case modeling many others have contributed to improving this technique, including Kurt Bittner, Alistair Cockburn, Gunnar Overgaard, and Geri Schneider.

During the 1990s use cases became one of the most common practices for capturing functional requirements. This is especially the case within the object-oriented community where they originated, but their applicability is not restricted to object-oriented systems, because use cases are not object oriented in nature.

Overview

Each use case focuses on describing how to achieve a goal or task. For most software projects this means that multiple, perhaps dozens, of use cases are needed to define the scope of the new system. The degree of formality of a particular software project and the stage of the project will influence the level of detail required in each use case.

Read more at Wikipedia.org