An association is a unidirectional relationship that describes a link between objects.
The UML standard does not explicitly display the direction of the association, and instead has the position of actors imply it. When an actor is positioned to the left of the use case, the association is an input, and when he is to the right, it is an output. To explicitly display the orientation of the association click Use Case Association in the Category tree, and select the Orientation option. For detailed information about working with display preferences, see Core Features Guide > Modeling with PowerDesigner > Diagrams, Matrices, and Symbols > Display Preferences.
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