Activity diagrams can also be drawn that cross several use cases, or that address just a small portion of a use case. The activity diagram of Figure 1 depicts one way to model the logic of the Enroll in University use case , a very common use of activity diagrams because they enable you to depict both the basic course of action as well as the alternate courses. Another way to depict this is shown in Figure 2 via the use of a normal activity although I don’t think this is as obvious as using a use case. To tell you the truth I’m not sure if this is official allowed by the UML but clearly it should be. This is a visual cheat that I use to indicate that an included use case is being invoked. In Figure 1 I indicated that the Enroll in Seminar use case is invoked as one of the activities. I prefer notes because stakeholders find them easier to understand. An alternative way to model this would have been with an OR constraint between the no match and applicant not on match list flows. Figure 2 includes a standard UML note to indicate that the merges does not require all three flows to arrive before processing can continue. This indicates that the process stops at this point. 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. The join waits for both to perform and continue.UML 2 activity diagrams are typically used for business process modeling, for modeling the logic captured by a single use case or usage scenario, or for modeling the detailed logic of a business rule. However, the Concurrent_Activity and result of decision between Activity 1 and Activity 2 (that merged into one output) are synchronize incoming concurrent flows. So, Activity 2 and Activity 3 are our alternate flows and only one of which will arrive. Why?: Otherwise, the join will wait for both flows. Merge should not be used to synchronize concurrent flows.Ī decision is used after a fork, the two flows coming out of the decision need to be merged into one before going to a join. Merge node is a control node that brings together multiple incomingĪlternate flows to accept single outgoing flow. Join nodes are introduced to support parallelism in activities. Outgoing edge and is used to synchronize incoming concurrent flows. Join node is a control node that has multiple incoming edges and one

Activity diagram uml