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This article will explain in detail the usefulness of the UML activity diagram for you. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

A brief introduction to UML activity diagrams

Activity diagram is another common tool used by UML to model the dynamic behavior of the system. It describes the sequence of activities, shows the control flow from one activity to another, and illustrates the workflow of business use case implementation. The business use case workflow illustrates what the business must do in order to provide the business protagonist with the value it needs. A business use case consists of a series of activities that together generate certain artifacts for the business protagonist. A workflow usually consists of a basic workflow and one or more alternative workflows, and the structure of the workflow is illustrated by an activity diagram. Workflow activity diagrams are used to study the sequence of tasks or activities to be performed to achieve business goals.

2. The constituent elements of the UML activity diagram (Activity Diagram Element):

1. The active state (Activity) is used to express the non-atomic operation in the state machine, and the active state can be decomposed into other sub-activities or action states.

2. The Actions refers to the atomic, uninterruptible action, and after the completion of this action, it changes to another state by completing the transition.

The icons of the active state and the action state in the UML activity diagram are the same, represented by smooth rounded rectangles.

3. Action state constraint (Action Constraints) is used to constrain the action state, showing the pre-conditions and post-conditions of the action state.

4. The conversion between Control Flow actions is called action flow. The conversion of the activity diagram is represented by a straight line with an arrow, and the direction of the arrow points to the direction of turning.

5. The Initial Node is represented as a solid black dot.

6. The termination node (Final Node) is divided into activity termination node (activity final nodes) and process termination node (flow final nodes). The activity termination node represents the end of the entire activity, while the process termination node represents the end of the subprocess.

7. The object node (Object node) is represented by rectangle.

8. The data storage object (DataStore) is marked with the keyword «datastore ».

9. The object stream (Object Flows) in the UML activity diagram is represented by a dashed line with arrows.

10. Branch and merge (Decision and Merge Nodes) branches and merges are represented by a diamond.

11. Bifurcation and confluence (Fork and Join Nodes) can be divided into horizontal wind direction and vertical direction. There may be two or more control flows running concurrently when an object is running. In order to model the concurrent control flow, the concepts of bifurcation and convergence are introduced in UML. Bifurcation is used to divide the action flow into two or more branches that run concurrently, while convergence is used to synchronize these concurrent branches in order to complete a transaction together.

Exception handling (Exception Handler) when an exception occurs in a protected activity, the exception handling node is triggered.

13. The activity interruption area (Interruptible Activity Region) revolves around some interruptible action state diagrams, which is actually a representation of exceptions.

14. Partition divides the activities in the activity diagram into several groups, and assigns each group to the business organization responsible for this group of activities, that is, objects. In the activity diagram, the swimming lane distinguishes the objects responsible for the activities, and it clearly indicates which activities are carried out by which objects. In an activity diagram that contains swimming lanes, each activity can only explicitly belong to one swimming lane. Swimming lanes are drawn with vertical solid lines, and the area separated by vertical lines is swimming lanes. The name of the swimming lane or the name of the object can be given at the top of the swimming lane, which is responsible for all the activities in the swimming lane. Swimming lanes have no order, activities in different swimming lanes can be carried out either sequentially or concurrently, and action flow and object flow are allowed to cross the separation line.

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