public static function delete_instance($workshopid) {
        global $DB;

        $dimensions = $DB->get_records('workshopform_rubric', array('workshopid' => $workshopid), '', 'id');
        $DB->delete_records_list('workshopform_rubric_levels', 'dimensionid', array_keys($dimensions));
        $DB->delete_records('workshopform_rubric', array('workshopid' => $workshopid));
        $DB->delete_records('workshopform_rubric_config', array('workshopid' => $workshopid));
    }