Activity Diagram
An Activity Diagram describes process options consisting of individual activities, which are described using steps and possible alternatives. It can be used for modeling business processes and system processes, with lanes enabling the modeled areas to be structured.
Activity modeling emphasizes the sequence and conditions for coordinating lower-level behaviors, rather than which classifier owns those behaviors. Generally speaking, Activity Diagrams are control flow and object flow models. The actions coordinated by activity models can be initiated because other actions finish executing, because objects and data become available, or because events occur external to the flow.