"A databse is not strictly a heirarchal tree."
Neither is a traditional UNIX file system. A UNIX filesystem is a directed graph. It's only the "no hardlinks to directories" heresy that's keeping you from being able to descibe arbitrary networks of relations in terms of filesystems: every table a directory, every key a link.
You can use symlinks instead of hardlinks, if you're scared of programs like "find" going all pear-shaped following hard links. Old school UNIX hackers aren't afraid of tickling the dragon's tail.
