Hi Pablo,
Internal communication:
When you save questionnaire BO an internal message will be created to the ServiceReqeustAux BO.
You would have maintained instance identification for the Receiver BO in .pid based on that it will try to find the instance, if the instance doesn't exists it will create else it will update.
Note: For instance identification if the node has multipliple cardinality, and if the instance identification returns more then one instance , then it will pick the first instance only.
Thanks, Pradeep.