In UML modeling, an action represents a discrete unit of executable functionality in an activity.
Actions have incoming and outgoing activity edges that specify the flow of control and data to and from other activity nodes. The actions in an activity begin to execute when all of the input conditions are met.
You can add input pins and output pins to specify values that are passed to and from the action when it executes. You can also define preconditions and postconditions, called constraints, for an action.
Each action has a unique name that describes the behavior.
As the following figure illustrates, an action is displayed as a rectangle with rounded corners that contains the name of the action.
Parent topic: Activity diagrams
Related concepts
Activities
Structured activities
Call behaviors
Call operations
Control nodes
Object nodes
Activity edges