Create a relationship object for this attribute from the given
        relator and relationship direction.

def make_relationship(self, relator,
                          direction=
                            RELATIONSHIP_DIRECTIONS.BIDIRECTIONAL):
        """
        Create a relationship object for this attribute from the given
        relator and relationship direction.
        """
        if IEntity.providedBy(relator): # pylint:disable=E1101
            rel = DomainRelationship(relator, self,
                                     direction=direction)
        elif IResource.providedBy(relator): # pylint:disable=E1101
            rel = ResourceRelationship(relator, self,
                                       direction=direction)
        else:
            raise ValueError('Invalid relator argument "%s" for '
                             'relationship; must provide IEntity or '
                             'IResource.' % relator)
        return rel