How is a UML Use Case Diagram different from a traditional flow chart?
As mentioned above, UCDs represent functionality in a top-down way, whereas flow charts represent behavior in a linear, time-based way. Also, the way you develop them is all-together different. Example: (This text refers to the diagrams below.) When constructing a UCD, the initial step is to identify all of the top-level behavior. Once you have done this (not a very tricky process) you have already described, at least in a high-level way, all of the things your system knows how to do. You can then continue to add detail by decomposing your use cases into more use cases which are used by the top-level use cases. At every stage of development, though, your UCD is a complete description of the system’s functionalty: it may lack detail, but it will not lack feature set elements. And if functionality or behavior is added or deleted over the life of your project, the scope of the change you need to make is proportional to both the scope of the change in the system itself, and the maturity of
