(c) Bruce Powel Douglass, Ph.D. 2019

Jun 29, 2018

Specific Parameters in a sequence Diagram

1 comment

Edited: Jun 29, 2018

When modeling a use case using a sequence diagram, do you use specific values for the values of parameters, or do you depict the parameters themselves? For example, suppose you have a message SetPosition. The message takes two parameters, PosX and PosY. When drawing a sequence diagram where 'A' calls 'B', which is preferred?


SetPosition(144, 25)




SetPosition(PosX, PosY)


Because it's a use case scenario, I thought using specific values like the first option would be preferred because you are illustraing a particular scenario. On the other hand, the second option is more generic and would apply to many scenarios. However, if you have a scenario, where the flow of control changes based on a particular parameters' value, the second option is not as obvious.


On checking the IBM Rational Harmony for SE Deskkbook 4.1, on page 94 for example, they use the second option. In the ALT frame, there is a check on the value of CardStatus for example.

Jul 1, 2018

You can do either, but I usually use the more general parameters, UNLESS interactions differ based on specific values being passed. For example if SetPosition(0,0) caused the system to reorient and reboot while SetPosition(1,1) just caused something to move, then I would show specific values. If every time, the interaction was the same, then I'd use the more general form SetPosition(X,Y).


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