def get_objective_bank_hierarchy_design_session(self):
raise Unimplemented()<EOL>
Gets the session designing objective bank hierarchies.

        return: (osid.learning.ObjectiveBankHierarchyDesignSession) - an
                ``ObjectiveBankHierarchyDesignSession``
        raise:  OperationFailed - unable to complete request
        raise:  Unimplemented -
                ``supports_objective_bank_hierarchy_design() is false``
        *compliance: optional -- This method must be implemented if
        ``supports_objective_bank_hierarchy_design()`` is true.*