Create Sub-category for my articles

I am interested in creating sub categories in my categories for my articles.  Does anyone have any ideas on how I can get this done.  I have been in my admin section and I can add categories, but I want to be able to make it more specific for searching.  Thanks,

This is out of default functional. You can`t do this in admin. But you can change functional (BxDolArticles.php) to realize your wishes.

Hi i have very interesting modification for Dolphin's articles. You will can look on it : http://www.boonex.com/unity/extensions/entry/Super_Article