Hi Pablo,
Internal communication:
When you save questionnaire BO an internal message will be created to the ServiceReqeustAux BO.
Based on the instance identification method maintained at each node level, it will try to find the instance from the sending BO data in the receiveing BO, if it exists it will update otherwise it will create new instance
Note: For the node with mutliple cardinality, if the instance identification returns more than one instance, then it will pick the first one only
In the WS approach you will have to do the following:
Create WS on BO ServiceReqeustAux ,
Download .wsdl file,
create .wsid on this .wsdl,
Create BeforeSave event on questionnaire BO and call the .wsid
where as internal communication you do the mapping between two BOs.
Thanks, Pradeep.