5. Functional modeling

While class and object diagrams can be used to explicitly represent the static structure of the system and model the concepts involved in its definition, they do not provide an acceptable answer when it comes to expressing the functional need to be met. What functions must the system perform? What services must it provide? What should its mission be within the organization in which it operates? These are all questions that express the problem from the user's point of view, and are therefore essential for expressing the need and specifying the expected system. To answer these questions, UML proposes to model system functionalities through use cases. This technique, developed and perfected by Ivar Jacobson, is the essential complement to class diagrams in a coherent object-oriented modeling approach.