In software and systems engineering, a use case is a list of action or event steps, typically defining the interactions between a role (known in the Unified Modeling Language as an ''actor'') and a system, to achieve a goal. The actor can be a human, an external system, or time. In 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 the Systems Modeling Language (SysML) or as contractual statements.
Use case analysis is an important and valuable requirement analysis technique that has been widely used in modern software engineering since their formal introduction by Ivar Jacobson in 1992. Use case driven development is a key characteristic of many process models and frameworks such as ICONIX, the Unified Process (UP), the IBM Rational Unified Process (RUP), and the Oracle Unified Method (OUM). With its inherent iterative, incremental and evolutionary nature, use case also fits well for agile development.
== History ==
In 1986, Ivar Jacobson first formulated textual, structural, and visual modeling techniques for specifying use cases. In 1992 his co-authored book ''Object-Oriented Software Engineering - A Use Case Driven Approach''〔Jacobson et al, 1992.〕 helped to popularize the technique for capturing functional requirements, especially in software development. Originally he had used the terms ''usage scenarios'' and ''usage case'' — the latter a direct translation of his Swedish term ''användningsfall'' — but found that neither of these terms sounded natural in English, and eventually he settled on ''use case''.〔
Since then, other experts have also contributed a great deal to the technique, notably Alistair Cockburn, Larry Constantine, Dean Leffingwell, Kurt Bittner and Gunnar Overgaard.
In 2011, Jacobson published an update to his work, called ''Use Case 2.0'',〔
〕 with the intention of incorporating many of his practical experiences of applying use cases since the original inception of the concept.〔(【引用サイトリンク】title=Business Analysis Conference Europe 2011 - 26-28 September 2011, London, UK )〕
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