def get_destination_types_by_relation_type(self, relation_type=None):
raise Unimplemented()<EOL>
Gets all destination ``Types`` related by the given type.

        arg:    relation_type (osid.type.Type): a relation type
        return: (osid.type.TypeList) - the destination types
        raise:  NullArgument - ``relation_type`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        *compliance: mandatory -- This method must be implemented.*