@abc.abstractmethod<EOL><INDENT>def get_grade_system_by_grade(self, grade_id):<DEDENT>
return<EOL>
Gets the ``GradeSystem`` by a ``Grade``  ``Id``.

        :param grade_id: ``Id`` of a ``Grade``
        :type grade_id: ``osid.id.Id``
        :return: the grade system
        :rtype: ``osid.grading.GradeSystem``
        :raise: ``NotFound`` -- ``grade_id`` not found
        :raise: ``NullArgument`` -- ``grade_id`` is ``null``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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