@abc.abstractmethod<EOL><INDENT>def get_source_types_by_relation_type(self, relation_type):<DEDENT>
return<EOL>
Gets all source ``Types`` related by the given type.

        :param relation_type: a relation type
        :type relation_type: ``osid.type.Type``
        :return: the source types
        :rtype: ``osid.type.TypeList``
        :raise: ``NullArgument`` -- ``relation_type`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

        *compliance: mandatory -- This method must be implemented.*