When comparing sequences, the following message parameters are used to determine whether the messages in the two sequence diagrams are identical:
One simple approach involves comparing the exact position of every message and stopping at the first difference. However, this is probably too naive a comparison. For example, if there is a time offset in one sequence diagram, this kind of comparison would stop at the first message.
A more useful approach, therefore, is to take all events (message departures and arrivals) in order, and compare them without using the exact time. This kind of comparison, although simple, still shows when two sequence diagrams are essentially identical.
Because some messages can be "noise," the comparison algorithm must also be able to decide whether a message is legitimate, and if not, mark it and continue with the comparison starting with the next message.
The point in comparing two sequence diagrams is not to show when one sequence is identical to another, but rather where and why they are different. Therefore, yes/no answers are not sufficient. Proper results must detail precisely what is identical and what is different. This approach is the approach that IBM® Rational® Rhapsody® takes when comparing message sequences.