Unified Modeling Language<\/a>, activity diagrams are intended to model both computational and organizational processes (i.e., workflows), as well as the data flows intersecting with the related activities. Although activity diagrams primarily show the overall flow of control, they can also include elements showing the flow of data between activities through one or more data stores.<\/p>\nActivity diagrams are constructed from a limited number of shapes, connected with arrows. The most important shape types:<\/p>\n
ellipses represent actions;
\ndiamonds represent decisions;
\nbars represent the start (split) or end (join) of concurrent activities;
\na black circle represents the start (initial node) of the workflow;
\nan encircled black circle represents the end (final node).
\nArrows run from the start to the end and represent the order in which activities happen.<\/p>\n
Activity diagrams can be regarded as a form of a structured flowchart combined with a traditional data flow diagram. Typical flowchart techniques lack constructs for expressing concurrency. However, the join and split symbols in activity diagrams only resolve this for simple cases; the meaning of the model is not clear when they are arbitrarily combined with decisions or loops.[citation needed]<\/p>\n
While in UML 1.x, activity diagrams were a specialized form of state diagrams, in UML 2.x, the activity diagrams were reformalized to be based on Petri net-like semantics, increasing the scope of situations that can be modeled using activity diagrams. These changes cause many UML 1.x activity diagrams to be interpreted differently in UML 2.x.[citation needed]<\/p>\n
UML activity diagrams in version 2.x can be used in various domains, e.g. in design of embedded systems. It is possible to verify such a specification using model checking technique.<\/p>\n
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