![]() ![]() A join may have two or more incoming transitions and one outgoing transition. Below the fork, the activities in each flow carry out in parallel.Ī join represents the synchronization of two or more concurrent flows of control. A synchronization bar is represented as a thick vertical or horizontal line.Ī fork may have one incoming transition and two or more outgoing transitions, each of which represents an independent flow of control. In UML, a synchronization bar is used to specify the forking and joining of these parallel flows of control. While modeling flow of control, it is common to encounter flows that are concurrent or parallel. Across all these outgoing transitions, guards should not overlap, but they should cover all possibilities. In UML, a branch is represented as a diamond.Ī branch may have one incoming transition and two or more outgoing transitions. Like in flowcharts, we can include a branch, which specifies alternate paths taken based on some Boolean expression which is also known as a guard condition. Therefore, as shown in the above figure, we can specify the initial state (solid ball) and stop state (a solid ball inside a hollow circle). In UML, a transition is represented as a simple directed line.Ī flow of control has to start and end someplace. This flow is represented as transitions to show the path from one action or activity state to the next action or activity state. When the action or activity completes, the flow of control passes immediately to the next action or activity state. There is no difference in the notation of activity states and action states except that the activity states may have additional information like entry and exit actions as shown below: Activity states are non-atomic and can be interrupted, considered to take some duration to complete. In contrast, activity states can be further decomposed, their activity being represented by other activity diagrams. In UML, an action states is represented using a lozenge symbol (rounded rectangle) as shown below: These atomic computations are called action states because they are states of the system, each representing the execution of an action. An activity diagram is like a flowchart, representing flow of control from activity to activity, whereas, the interaction diagrams focus on the flow of control from object to object.Īctivities result in some action, which is made up of executable atomic computations that result in a change of state of the system or the return of a value.Īctions involve calling another operation, sending a signal, creating or destroying an object or some pure computation, such as evaluating an expression.Īn activity diagram shares the same common properties as do all other UML diagrams like a name which is used to uniquely identify the diagram and the graphical content which is a projection into the model.Īctivity diagram may represent actions which are atomic computations.
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