Oh, I see now, I was under the impression that there was an instance of Link for each pair of communication ↔ group, (like the table used by the many-to-many links).
But the one-to-one or many-to-one links are just a method on communication that will look for the instance of Group that has the “id” == “communication.groupId”. Sort of, right?
Thank you very much joshOntologize. All set and running 
