Activity diagrams are similar to flowcharts and are a model view used to describe the behavior of a system. They can be used to describe the workflow and concurrent behavior of a system, showing the sequence of activities performed by objects participating in a certain behavior of the system, and are another form of state machine representation.
Activity diagrams are used to analyze processes, utilizing visualization tools to depict the operation of specific real-world tasks, producing content that is both easy for people to understand and convenient for computer development and implementation.
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An activity diagram is centered around activities, with rounded rectangles representing activities. Transition lines usually do not contain content, except when making judgments, where the condition is written on the line.
A state diagram is centered around states, with rounded rectangles representing states. The content written on the transition line corresponds to the activities in the activity diagram.
Starting Point: An activity diagram begins with a starting point, represented by a solid circle.
Activity: Represents a step or task in the system or business process, indicated by a rounded rectangle with the activity name inside.
Decision: Represented by a diamond shape, also known as branching and merging. A decision has one incoming path and two or more outgoing paths.
Synchronization: Represented by a solid narrow rectangle, also known as fork and join, used to describe parallel processes. A fork indicates the start of parallel activities, while a join indicates the end of parallel activities.
Swimlane: Swimlanes group activities or actions by the executing entity, with each group separated by swimlanes. This clearly describes the transfer of activities or actions and clarifies who completes them.
Object Flow: Represented by a rectangular box for an object, with dashed arrows indicating the dependency between activities and objects.
The granularity of all activity nodes should be roughly the same:
“Logging into the system” and “Clicking a button” appearing together is incorrect.
“Entering username and password” -> “Verifying identity” -> “Entering the main interface” is correct.
At the same time, there are two or more concurrent control flows. A fork indicates a control flow splitting into two or more concurrent control flows, while a join indicates synchronization of two or more concurrent control flows.
In an activity diagram, synchronization bars are used to illustrate the forking and joining of these control flows, represented by solid narrow rectangles.
Business Process Modeling: Procurement approval, leave process
System Function Operation Flow Modeling: Login, order placement, report generation
Behavior Modeling of Classes (in conjunction with state diagrams): User registration process, order processing process
Concurrent or Collaborative Behavior Modeling: Multithreaded collaboration, task distribution
1. Keep the graphics simple and avoid excessive nesting
2. Clearly identify the executor of each action
3. Use decision and concurrency structures appropriately
4. Can be used in conjunction with other UML diagrams
In an activity diagram, there is only one initial point, but there may be multiple end points.
Activity diagrams require activity naming to follow verb-object phrases, avoiding issues like treating objects as activities or unclear operation objects.
No. Typically, forks and joins coexist, but there are situations where only forks exist without joins.
Swimlanes group activities or actions by the executing object, using lanes to separate each group. This clearly describes the transfer of activities or actions and clarifies who completes these activities or actions.
Each swimlane is named after the object's name or the actor's name, and these names are unique within an activity diagram.
1. From top to bottom, from left to right
2. Align activities as much as possible
3. Avoid crossing activity lines
4. Limit the number of activities to 10-15
1. Activity diagrams can represent concurrent activities, whereas flowcharts cannot.
2. Activity diagrams are object-oriented, whereas flowcharts are process-oriented.
3. Activity diagrams describe the rules followed by the sequence of object activities, focusing on system behavior rather than the processing process; flowcharts focus on describing the processing process, with their main structure being sequence, branching, and looping, with strict order and timing relationships between processes.
1. Activity diagrams are technical, a type of dynamic view in UML modeling, usually used in the design phase of software systems, and are a diagram for participant communication. BPMN is business-oriented, used to describe program execution processes, can generate executable declaration files, and can be used for dynamic execution by process engines;
2. As a whole, BPMN diagrams are easier for business stakeholders to understand than activity diagrams;
3. BPMN contains special modeling elements that make it more suitable for business purposes. Activity diagram modeling elements are relatively simpler and more singular;
4. BPMN models B2B interactions better than activity diagrams.