The use case model is used to illustrate and document the expectations that users have for the system.
For this reason, the use case model has become a popular addition to nearly all the object-oriented development methodologies.
The expectations expressed by the use case model create a focus or target for subsequent analysis and design efforts.
Even if the use case model is not perfect or complete, it will help steer the analysis process by providing a reference point for questions and decisions.
Done well, the use case model provides a solid foundation for finding objects, developing test cases, modeling work and screen flows, and defining the behavior of the system. The fundamental elements of the use case model are covered in this module. This module will also identify detailed scenarios for developing and testing the behavior of the system.
The Use Case diagram is a unique graphical element, in that it is a diagram used to model how people expect to use a system. The diagram describes who the relevant users will be, the services they require of the system, and the services they need to provide to the system. The Use Case diagram can be applied to many types of development, including manual systems, but it is most commonly used for systems and subsystems.
The Use Case diagram is the key element of the Object-Oriented Software Engineering
(OOSE) method, also known as Objectory (short for object factory), published in 1992 by Ivar
Jacobson. The technique had a proven track record with large-scale object-oriented projects at Ericsson and other companies.
Its success caught the attention of authors of other popular methods that lacked a means to document system requirements from
the viewpoint of clients and other systems.
Many of the leading methodologists like Grady Booch and James Rumbaugh, sought to find ways to merge their methods with this usecase-driven approach. As a result, the Use Case diagram was formally incorporated into UML 0.9, released in June 1996.
The Use Case Diagram
is often used as part of a more comprehensive use-case-driven approach that also includes a textual description of individual use cases and the extraction of scenarios. The textual description addresses the detailed requirements for a use case. Scenarios address the need to explore options in the execution of the use case, to test the requirements, and to provide a high-level test plan for subsequent development phases. Three Core diagrams of the use case approach are
- the Use Case diagram,
- the use case narrative or description, and
- the use case scenario (using an Activity diagram).