What is a Use Case?
A use case is a description of a scenario in which a user will engage with a product or system. It serves as the basis for analysis how the system is (or may be) used and provides a framework for identifying the requirements for system development. The Project Management Institute (PMI) articulates it as “a description of all the ways an end-user wants to ‘use’ a system.” In this case, “uses” are viewed as “requests of the system” while use cases refer to the system’s responses to these requests.
Popularized by renowned software engineer Ivar Jacobson, use cases offer an effective approach for gathering and organizing requirements of systems. They are explained at length in the 2000 book, “Writing Effective Use Cases,” by Alistair Cockburn.
Use Case Diagram vs. Use Case Model
Use cases are commonly presented in Unified Modeling Language (UML) as diagrams. But these aren’t as helpful as they can potentially be. That brings us to the need to distinguish between use case diagrams and use case models.
A use case diagram is a depiction of the user’s interaction with a system. It portrays the user and the different use cases that they are involved in. It features the system, the actors, and the use cases.
The use case model, on the other hand, comprises a use case diagram and narrative text describing the use cases or flow of events. These textual descriptions, which are not standardized in UML, make use of case models more useful for projects.
Use Case Diagram Components
There are three main components of use cases and these have already been mentioned above. They are:
The system – This refers to the totality of the solution that you look to create. The limits of the system are defined by a boundary box in a use case diagram.
Actors – You can think of these as people (roles), systems, or time. People actors are role players in the system – they are viewed based on roles rather than job titles. System actors are sub-systems or other devices that are critical to the function of the overall system. Time actors may be thought of as triggers of activities that are based on time.
Use cases – These are the processes or series of actions that take place within the system.
Interfaces constitute a supporting component. They drive the interaction between actors and the system.
How Use Cases Help for Projects
Use cases provide a useful structure for gathering requirements and one that aids discussions on them. It can also create room for incorporating changes as your understanding of a project broadens. A key benefit of use cases is that they make it easier to know and effectively manage project scope. This is a critical starting point in project management and is sometimes regarded among the most difficult to do. As new use cases emerge, the use case diagram helps to know if and how they fit in and what extra work will be needed.
This model can also go a long way in helping to manage risks. It can lessen the risk of getting requirements wrong, for instance, especially concerning how they’re interpreted. Use cases help to thoroughly evaluate risks, including new technology and an increasing number of actors, and tackle them in the right order.
