I almost always draw flowcharts or activity diagrams rather than rely on text alone. Remember that visual models are almost always easier to test and interpret than textual models. As someone once said, "When in doubt, draw a picture."
An Activity Diagram is a type of diagram in the Unified Modeling Language.
Activity diagrams represent the business and operational workflows of a system. An Activity Diagram shows the overall flow of control.
In UML 1.x, an Activity diagram is a variation of the UML State diagram where the "states" represent operations, and the transitions represent the activities that happen when the operation is complete.
The UML 2.0 Activity diagram, while similar looking to the UML 1.x Activity diagram, now has semantics based on Petri nets.
In UML 2.0, the Interaction Overview diagram is based on the Activity diagram.