what is use case diagram in software engineering , In software engineering, a use case diagram (UCial) is a diagram that delineates the key functionality of an application or system by using user stories. User stories are small, simple descriptions of how a user will interact with the system. Each use case is represented by a rectangle, with each edge corresponding to one of the user story’s ENoelements. The tallest rectangle corresponds to the most important function or “feature”; typically, this is the use case that provides the overall goal of the system. A use case may also have child use cases (represented by smaller rectangles) that further refine its functionality.
Typically, the structural layers in an application are depicted on the bottom of a UCial; these layers typically correspond to architectural levels in an organization’s development process. As design changes are made and more functions are added to the application, it becomes necessary to update and modify the UCial. The steps involved in doing so are called “mapping.” The act of updating and modifying a UCial is called “UXing.”
