Use cases are used to model single tasks that a user of the system may perform. They give a slightly more complex definition of the process involved in a system that conforms to the requirements laid down.
Common uses of use cases:
- To define the scope of the system.
- To define the people and other systems that will use the system.
- To document the way the business process is performed.
- Used by Test Analysts as part of the documentation reviewed when creating test cases.
- To provide the basis for the User Documentation: help system or manuals/user guides.
Use Case diagrams describe how a user of the proposed system will interact with this system to perform a discrete unit of work. It describes a single interaction over time that has meaning for the end user.
Along with the diagrams in a use case, a textual flow should also be included. Both the diagrams and the textual flow should include the main path and all alternate paths.
There should also be section that documents exception flows. Exception flows (error handling). The wording of the error message should be included in these flows.
Use cases typically have requirement and constraint definitions associated with them. These describe the essential features and rules under which the use case will operate.
You should include a glossary in the use case document – this allows you to enter terms and their definitions or descriptions directly into the use case so readers do not need to refer back to other documentation (such as the BRD) to verify what a certain definition is. Having a common and shared description of a term is important when relating new concepts to other parties involved in the system development process.