Cases

In software engineering and system engineering, a use case is a technique for capturing functional requirements of systems and systems-of-systems. more...

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Each use case provides one or more scenarios that convey how the system should interact with the users called actors to achieve a specific business goal or function. Use case actors may be end users or other systems. Use cases typically avoid technical jargon, preferring instead the language of the end user or domain expert. Use cases are often co-authored by business analysts and end users.

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 orginated use case modeling many others have contributed to improving this technique, including Kurt Bittner, Alistair Cockburn, and Gunnar Overgaard.

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.

Scope and goals of a use case

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 embrace 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.

Use cases should not be confused with the features of the system under consideration. A use case may be related to one or more features, a feature may be related to one or more use cases.

A use case defines the interactions between external actors and the system under consideration to accomplish a goal. An actor is a role that a person or thing plays when interacting with the system. The same person using the system may be represented as two different actors because they are playing different roles. For example, "Joe" could be playing the role of a Customer when using an Automated Teller Machine to Withdraw Cash, or playing the role of a Bank Teller when using the system to Restock the Cash Drawer.

Use cases treat the system as a black box, and the interactions with the system, including system responses, are perceived as from outside the system. This is a deliberate policy, because it forces the author to focus on what the system must do, not how it is to be done, and avoids the trap of making assumptions about how this functionality will be accomplished.

Read more at Wikipedia.org