code: def _set_relationship_type(self, type_identifier, display_name=None, display_label=None, description=None, domain='Relationship'):
          
          if display_name is None:
              display_name = type_identifier
          if display_label is None:
              display_label = display_name
          if description is None:
              description = 'Relationship Type for ' + display_name
          self._relationship_type = Type(authority='DLKIT',
                                         namespace='relationship.Relationship',
                                         identifier=type_identifier,
                                         display_name=display_name,
                                         display_label=display_label,
                                         description=description,
                                         domain=domain)
docs: Sets the relationship type