UML Activity Diagrams

Activity Diagram

• An activity diagram is a type of UML diagram that describes the dynamic aspects of a system, representing the flow from one activity to another.
• It is a visual representation of a series of actions or flow of control in a system, similar to a flowchart or a data flow diagram.

Key Features

• Activity diagrams deal with all types of flow control, including sequential, branched, and concurrent flows.
• They use different elements such as fork, join, and decision nodes to represent complex flows.

Benefits

• Activity diagrams help demonstrate the logic of an algorithm, describe the steps in a use case, and illustrate business processes or workflows.
• They simplify and improve processes by clarifying complicated use cases and model software architecture elements.

Difference from Flowcharts

• Flowcharts are a primitive version of activity diagrams, used by non-programmers to model workflows.
• Activity diagrams are used by developers to depict workflows, understand the flow of programs, and figure out constraints and conditions.

Notations

• Initial State/Start: a small filled circle followed by an arrow, representing the start point of an activity diagram.
• Activity or Action State: a rectangle with rounded corners, representing a non-interruptible action of objects.
• Action Flow: an arrowed line, illustrating the transitions from one action state to another.
• Decisions and Branching: a diamond, representing a decision with alternate paths, labeled with conditions or guard expressions.
• Guards: a statement written next to a decision diamond, specifying a condition that must be true before moving to the next activity.
• Synchronization: a fork node, used to split a single incoming flow into multiple concurrent flows, and a join node, joining multiple concurrent flows back into a single outgoing flow.