Virtual Method calls in a Sequence Diagram

[JohnWSaundersIII]

I have a piece of code which uses a factory to create an instance of the appropriate derived class given the input parameters to the factory. The code then needs to call a virtual method of whichever derived class instance.

How do I show this on an Interaction diagram? I couldn't figure out how to do it with an "alt" fragment, for instance.

Thanks,
John Saunders

[TrtnJohn]

I'd like to know the best way to do this too.  I noticed there is a insert as New Child (Generalization) in the paste menu when you drag a class into the diagram.  But, it is grayed out in my version.  I'd like to have a lifeline for each child class so I can show which virtual method in which class is used.

[sargasso]

I think, from memory when I went through this about a year ago I had to actually create a "sample" code and work backwards to the seq diagram.  IIRC it was tricky.  IIalsoRC the trick was to remember to work with real instances in the diagrams.

I dont have the result sorry - dont work there no more.

bruce

[TrtnJohn]

When showing a generalization, there is only one instance and multiple classes involved.  This is where my confusion comes.  If you want to show the order of virtual method calls you really need a lifeline for each derived class.  But these classes are really only part of a single object instance.  When diagramming use case scenarios the single instance is all that matters.  But, at times, I use the sequence diagram to document code flow.  This is when it would be nice to show the virtual calls.

[sargasso]

Sorry I wasn't clear enugh.  I meant that I had to go back through modelling the exact instances to come up with the generalised case.

bruce