UML 2 Interaction Overview Diagram

Interaction Overview Diagrams
An interaction overview diagram is a form of activity diagram in which the nodes represent interaction diagrams. Interaction diagrams can include sequence, communication, interaction overview and timing diagrams. Most of the notation for interaction overview diagrams is the same for activity diagrams. For example, initial, final, decision, merge, fork and join nodes are all the same. However, interaction overview diagrams introduce two new elements: interaction occurrences and interaction elements.

Interaction Occurrence
Interaction occurrences are references to existing interaction diagrams. An interaction occurrence is shown as a reference frame; that is, a frame with "ref" in the top-left corner. The name of the diagram being referenced is shown in the center of the frame.

Interaction Element
Interaction elements are similar to interaction occurrences, in that they display a representation of existing interaction diagrams within a rectangular frame. They differ in that they display the contents of the references diagram inline.

Putting it all Together
All the same controls from activity diagrams (fork, join, merge, etc.) can be used on interaction overview diagrams to put the control logic around the lower level diagrams. The following example depicts a sample sale process, with sub-processes abstracted within interaction occurrences.