What is an interaction diagram? As its name might suggest, an interaction diagram is a type of UML diagram that's used to capture the interactive behavior of a system. Interaction diagrams focus on describing the flow of messages within a system, providing context for one or more lifelines within a system.

Interaction diagrams are models that describe how a group of objects collaborate in some behavior - typically a single use-case. The diagrams show a number of example objects and the messages that are passed between these objects within the use-case.