[Magritte] Relation description with instances of a class

Hi Is it possible to use existing descriptions to express a relation with object existing or not ? We could imagine choosing a responsible from an existing list of person defined by a class Person. If the person doens't exist, we can instanciate a new one. I will try to create an appropriate description but I don't really know where to subclass as it is a bit of a mix between a SingleOptionDescription with instances of a class as option and a ToOneRelation description with class Person. What do you think ? I ve tried with a MASingleOption description defining the reference as Person description and options as my repository of users but that hangs (due to the reference wich is a Caontainer Description I guess)... I also tried with MADynamicDescription without result... that makes me ask another question... Are all MADynamicObject used with classes or subclasses as it is in my image ? thanks Cédrick