In Figure 2 the Enroll In Seminar activity includes this symbol. The rake in the bottom corner of an activity, such as in the Apply to University activity, indicates that the activity is described by a more finely detailed activity diagram. Figure 2 is organized into three partitions, also called swimlanes, indicating who/what is performing the activities (either the Applicant, Registrar, or System). The implication is that one or more incoming flows must reach this point until processing continues, based on any guards on the outgoing flow. A diamond with several flows entering and one leaving. The flows leaving include conditions although some modelers will not indicate the conditions if it is obvious. A diamond with one flow entering and several leaving. Text such as on a flow, defining a guard which must evaluate to true in order to traverse the node. This denotes the end of parallel processing. All flows going into the join must reach it before processing may continue. A black bar with several flows entering it and one leaving it. This denotes the beginning of parallel activity. A black bar with one flow going into it and several leaving it. 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. An activity may be physical, such as Inspect Forms, or electronic, such as Display Create Student Screen. The rounded rectangles represent activities that occur. An activity diagram can have zero or more activity final nodes. The filled circle with a border is the ending point. An initial node isn’t required although it does make it significantly easier to read the diagram. ![]() The filled in circle is the starting point of the diagram. ![]() In many ways UML activity diagrams are the object-oriented equivalent of flow charts and data flow diagrams (DFDs) from structured development.Let’s start by describing the basic notation (there’s more) that I’ve used in Figures 1 and 2: Although UML activity diagrams could potentially model the internal logic of a complex operation it would be far better to simply rewrite the operation so that it is simple enough that you don’t require an activity diagram. UML 2 activity diagrams are typically used for business process modeling, for modeling the logic captured by a single use caseor usage scenario, or for modeling the detailed logic of a business rule.
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