578 Appendix A A.7 ACTIVITY DIAGRAM The activity diagram is used to model behavior in terms of the flow of inputs, outputs, and control. An activity diagram is similar to a traditional functional flow diagram. Table A.14 Activity Diagram Structural Nodes Diagram Element Activity Parameter Node act <Activity> Notation Description Activity parameter node symbols are rectangles that straddle the boundary of the activity frame. Other annotations include: «noBuffer», «optional», «overwrite», «continuous», «discrete», {rate=<Expression>}. Parameters can be organized into parameter sets, indicated by a bounding box around the parameters in the set. Parameter sets may overlap, and may have an annotation: {probability=<Expression>}. Section 9.4.1 <Parameter>:<Type>:<Multiplicity> <Parameter>:<Type>:<Multiplicity> Interruptible <InterrruptibleRegion> An interruptible region groups a subset of the 9.8.1