With practice, many required sequences of interactions can be implied from the class diagram, especially when class archetypes and stereotypes are used to indicate particular patterns of behavior and interaction. UML interaction diagrams make those implications explicit and describe clearly scenarios in which the sequence of interactions is not clear from class diagrams. In other words, UML interaction diagrams complement the more static nature of UML class diagrams by making explicit the dynamic interactions involved.
Neither type of diagram is particularly good at showing recursion and the handling of exceptions. For significant interactions of this type, it is best to attach a note to the relevant points in the diagram.
In the last article in the series, we will look briefly at the other five UML diagram types. Until then, I leave you with a quote from Peter Coad (et al):
"Why use scenarios [interaction diagrams]? Here's why:
To find additional objects.
To better distribute and refine responsibilities.
To gain a better understanding of system dynamics.
To assess model completeness.
To test an object model (ultimately, to test the system itself)."4