Refining Use Cases with Activity Diagrams

In a previous post, I discussed text based use case descriptions. This post discusses a graphical method:  activity diagrams.

Before discussing the advantages of refining use cases with activity diagrams, let's define activity diagrams.  One of my colleagues describes them as "flow charts on steroids."  Activity diagrams show the possible sequences of activities and the flow of data between activities in a single view.

The rectangles with rounded corners represent activities.  In the software world, an activity would be implemented as a functions or method.  On this diagram, the dashed red lines represent the order  that the actions occur.

Unlike text, graphical activity diagrams are not open to interpretation.  Even people not trained in UML's or SysML's subtleties understand an activity diagrams flowchart-like structure.  Complicated concepts, including exception condition handling, become clear when viewed on a single page.


Note that you may use nested activity diagrams (not what they are called, we'll get to the proper name later) to describe complex actions.

 In summary, the advantages of using activity diagrams to refine use cases include:

• Graphical representation is not open to interpretation the way text is
• Shows multiple paths (including exception conditions) in one view
• Complex actions may be further refined with other activity diagrams