The Interaction group is used for Interaction diagrams (Sequence, Timing, Communication or Interaction Overview), which are used to model work flow and sequential passing of messages between elements in real time.
Interaction diagrams are often placed beneath Use Case elements to further expand on Use Case behavior over time.
The Interaction group is used to model dynamic interactions between elements at run-time. The Actor element models a user of the system, while the other elements model things within the system, including standard elements (Lifeline), user interface component (Boundary), controller and Entity. The meaning of the element symbols is discussed further in the Sequence diagram topic. The Message (sequence) relationship is used to model the flow of information and processing between elements.
To add an element to the current diagram, click on the required icon, and drag it into position on the diagram. Set an element name and other properties as prompted.
To add a relationship, click on the required icon, then click on the start element in the diagram and drag to the end element.