There is few purpose of an activity diagram; one is to model a task (modeling).  Two, it is used to describe a function of a system represented by a use case.  It is also use to describe the logic of an operation.  And last but not least is to model the activities that make up the life cycle in the Unified Process.

            Activity diagrams have few notations that may help us in modeling process.  It involves Actions, Control Flows, Initial Mode, Decision Mode, Guard conditions and Final...