Dealing with Constraint {} in a plug-in

Hi,

Unfornately I’m french and so I don’t speak well english.
I’ll try to explain my problem.

I’m working on a ORM transformation plug-in (sorry but the Visual paradigm ORM isn’t complete…).
My problem is that I don’t know how to catch my “Constraint” between association.

I share you a picture for example:

Thanks for the help.
MCD_representation_XOR.png