protected function validate_item($item) {

        $allowed = array(
            'user'              => true,
            'grouping'          => true,
            'group'             => true,
            'role'              => true,
            'file'              => true,
            'scale'             => true,
            'outcome'           => true,
            'grade_item'        => true,
            'question_category' => true
        );

        if (!isset($allowed[$item])) {
            throw new coding_exception('Invalid inforef item type');
        }
    }