Activity diagrams are typically used for business process modeling, for modeling the logic captured by a single use case or usage scenario.


Initial node. The filled in circle is the starting point of the diagram.  An initial node isn’t required although it does make it significantly easier to read the diagram.
Activity final node. The filled circle with a border is the ending point.  An activity diagram can have zero or more activity final nodes
Activity.   The rounded rectangles represent activities that occur. An activity may be physical, such as Inspect Forms, or electronic, such as Display Create Student Screen.
Flow/edge.  The arrows on the diagram.  Although there is a subtle difference between flows and edges I have never seen a practical purpose for the difference although I have no doubt one exists.  I’ll use the term flow.
Fork.  A black bar with one flow going into it and several leaving it.  This denotes the beginning of parallel activity.
Join.  A black bar with several flows entering it and one leaving it.  All flows going into the join must reach it before processing may continue.  This denotes the end of parallel processing.
Condition.  Text such as [Incorrect Form] on a flow, defining a guard which must evaluate to true in order to traverse the node
Decision. A diamond with one flow entering and several leaving.  The flows leaving include conditions although some modelers will not indicate the conditions if it is obvious.
Merge.  A diamond with several flows entering and one leaving.  The implication is that one or more incoming flows must reach this point until processing continues, based on any guards on the outgoing flow.


  • Partition. is organized into three partitions, also called swimlanes, indicating who/what is performing the activities (either the Applicant, Registrar, or System).
  • Sub-activity indicator.  Indicates that the activity is described by a more finely detailed activity diagram.  
  • Flow final.  The circle with the X through it.  This indicates that the process stops at this point