Thank you, gideon.
> But a question: how are the initial tags set up if users can't ever define new ones?
Yes, It is also a problem. Since it cannot set up from a management screen like a category now, it adds to database directly or supplies example question.
I would like to use category and tag as key and to take a Q2A record into an external system. Example... RSS or PHP function(get_posts() of WordPress).
$args = array('category_name'=>$cats, 'tag'=>$tags);
$posts = get_posts($args);