Action (UML)

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An action (. English Action ) is a model element in the Unified Modeling Language (UML), a language for the modeling of the structures and the behavior of software - and other systems.


An action is an abstract model element in the UML2 metamodel . It represents an elementary building block for the specification of the behavior of a system.

An action receives input values ​​via input pins and produces output values ​​on output pins . The input and output pins are the hinges on which an action can be combined with other actions, so that the values ​​on the output pins of one action become the values ​​on the input pins of the other action. Behavioral descriptions such as the activity or the interaction orchestrate elementary actions for behavioral specifications.

The UML2 defines a set of elementary actions and divides them into several groups.

Call actions

Call actions include the action to call an operation on a class ( CallOperationAction ), the action to call the behavior of a class ( CallBehaviorAction ), the actions to send a signal ( SendSignalAction and BroadcastSignalAction ) and the action to send an object ( SendObjectAction ).

Actions to manipulate objects

Actions for manipulating objects include actions to create and destroy an object ( CreateObjectAction or DestroyObjectAction ) and to test the identity of an object ( TestIdentityAction ).

Actions for manipulating structural features

A set of actions is predefined for manipulating structural features . This includes an action to read a structural feature ( ReadStructuralFeatureAction ), to delete the contents of a structural feature ( ClearStructuralFeatureAction ) and to manipulate the contents of a structural feature ( AddStructuralFeatureValueAction and RemoveStructuralFeatureValueAction ).

Actions for manipulating object relationships

The actions for manipulating object relationships ( left ) include an action for creating and deleting an object relationship ( CreateLinkAction or DestroyLinkAction ), an action for reading an object relationship ( ReadLinkAction ), and an action for all object relationships to a specific one Association can be deleted ( ClearAssociationAction ).

Actions on objects

Some actions are provided in UML2 to get information about objects or to trigger the behavior of objects. ReadExtentAction makes all instances of a specific classifier available on the output pin . ReadIsClassifiedObjectAction determines whether an object is a direct or indirect instance of a particular classifier. The ReclassifyObjectAction action is available to make an object an instance of another classifier at runtime . StartClassifierBehaviorAction starts the classifier behavior of an instance.

Actions to Receive Events

The AcceptEventAction action receives an event , AcceptCallAction an event that indicates that an operation has been called.

Actions for generating a value

The ValueSpecificationAction action generates a certain value on an output pin according to a value specification.


Notation of an action as a rectangle with rounded corners
Special notations for four types of actions