protected function define_workshop_subplugin_structure() {

        // create XML elements
        $subplugin = $this->get_subplugin_element(); // virtual optigroup element
        $subplugin_wrapper = new backup_nested_element($this->get_recommended_name());
        $subplugin_table_settings = new backup_nested_element('workshopeval_best_settings', null, array('comparison'));

        // connect XML elements into the tree
        $subplugin->add_child($subplugin_wrapper);
        $subplugin_wrapper->add_child($subplugin_table_settings);

        // set source to populate the data
        $subplugin_table_settings->set_source_table('workshopeval_best_settings', array('workshopid' => backup::VAR_ACTIVITYID));

        return $subplugin;
    }