Beginning C# 2008 Objects: From Concept to Code

11.2. Scenarios

Events originating externally to a system occur randomly; we can't predict, for example, when a user will click a button on a GUI. For a system to perform useful functions, however, the internal events that arise in response to these external events—in other words, the messages that objects exchange in carrying out some system function—can't be left to occur randomly. Instead, they must be orchestrated in such as way as to lead, in a cause-and-effect fashion, to some desired result. In the same way that a musical score indicates which notes must be played by various instruments to produce a melody, a scenario prescribes the sequence of internal messages (events) that must occur in carrying out some system function from beginning ...