Joomla native routing is not quite robust and you can't control how the SEF URL of menu item is built. You can only define menu item alias - a component of URL.

By default aliases of Joomla menu items are relative: aliases of all parent menu items are auto-prepended to SEF URL.

So child menu items have URLs like:

http://site.com/parent-menu-item-alias/child-menu-item-alias

This plugin allows you to switch alias to 'direct' mode and have short URL without aliases of parent menu items:

http://site.com/child-menu-item-alias

Additionally to the functionality of Direct Alias (free extension) you can remove menu items' aliases from article URLs and leave only single article alias.

So instead of

http://site.com/news/34-article-alias

you will get

http://site.com/34-article-alias or http://site.com/article-alias if IDs are removed.

Active menu item is still identified, hence current menu item is highlighted in menu modules and modules are displayed correctly. Direct article menu items are preserved and have original native URLs unchanged.

Previous native URLs are redirected to new URLs with 301 status, hence search engines index is preserved.

Plugin adds only a single database query if a page is loaded via single article shortened URL. It's a nice and simple alternative to monstrous 3rd-party SEF extensions.