An Interaction is a unit of Behavior focusing on the observable exchange of information between connectable elements, a specialization of Interaction Fragment and of Behavior.
An Interaction originates in a modeling tool while creating Communication and Sequence diagrams. When you double click on an Interaction, a diagram is opened.
In the element dialog box, you can modify the current element and add various specifications to it. For more information about element dialog boxes and panes of the element dialog boxes, click here.
To open the Interaction dialog box, choose the Specification command from the Interaction shortcut menu.
In the Interaction dialog box, the Messages pane lists Messages contained in this Interaction.