Use cases are the tools which describes the behavior and how the user interacts with the system to perform some activity. In other words, it is a series of interactions between user and system that helps user to achieve the system goals. Use cases are simple because they only focus on business process at a time and used to gather the requirements by communicating with the stakeholders to write the system. Use case specification defines information that pertains to particular use case which is essential in understanding the purpose behind use case. It has one or more flow of activities associated with it. Use cases focus on only one business process at a time.
Iteration is an essential process while creating use case that undergoes continuous testing and refinement in the entire lifetime of a project. Because, users frequently change their minds about use cases and what to include. So, the analyst must have to perform iterations until the user believe that sufficient number of use cases are documented. This is done by building up the three stages little by little. Firstly, analyst creates functional representation of the system by working with user. Secondly, analyst builds the structural representation of the evolving system. Finally, using structural and functional representation, analyst creates behavioral representation of the evolving system which is use case representation. As working with user, the analyst performs iteration over each stage until the complete representation satisfied by the user. Iteration performs vital role in successful completion of the project.