docs: def set_id(self,my_id):
          """
          Sets the opinion identifier
          @type my_id: string
          @param my_id: the opinion identifier
          """
          if self.type == 'NAF':
              self.node.set('id',my_id)
          elif self.type == 'KAF':
              self.node.set('oid',my_id)