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UML Basics Introduction to UML Activity Diagrams

UML activity diagram

An activity diagram is a representation of an active view (see Figure 7-1). It includes handy shorthand notation that can be used for virtually any state diagram, although mixed representations of activity diagrams and state diagrams are ugly most of the time.

The active state is represented as a rectangle with rounded edges, which contains a description of the activity (normal state boxes have straight edges and rounded corners). Simple completion of the transformation is indicated by arrows. Branches represent converted guardianship conditions or diamonds with multi-labeled exit arrows. The bifurcation and combination of controls is the same representation as in the state diagram, which is multiple arrows entering or leaving the dark sync bar. Figure 7.1 shows the activity diagram for order processing.

Figure 7 - 1 UML activity diagram

In order to indicate a situation in which an external event must be included, the reception of an event can be represented as a trigger for a transition or as a special embedded symbol waiting for a signal. Transmission can be expressed in the same way. However, if there are many event-driven transitions, a generic state diagram representation is preferable.

1. Lane

It is often useful to organize activities in a model according to responsibilities. For example, all activities handled by a business organization can be organized. This allocation can be represented by organizing activities into distinct areas separated by lines. Because of their appearance, these areas are called lanes. Figure 7 - 2 shows the lane.

Figure 7 - 2 Lane and object flow

2. object flow

UML activity diagrams can represent the value flow and control flow of objects. Object flow states represent objects that are input or output from an activity. For output values, dashed arrows point from activity to object flow state. For input values, dashed arrows point from object flow state to activity. If the activity has multiple output values or subsequent control flows, the arrow faces away from the bifurcation symbol. Similarly, the multi-input arrow points to the union symbol.

Figure 7 - 2 shows an activity diagram with both activity and object flow states assigned to swimlanes.

UML activity diagrams and other diagrams

The activity diagram does not show all the details of the computational process. They represent the flow of activities but not the objects performing the activities. Activity diagrams are the starting point for design work. To complete the design, each activity must be expanded into one or more operations, each of which is assigned to a specific class. The result of this assignment leads to design work to implement the congruence of the activity diagram.

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