Maybe get them a copy of Craig Mullins book, Database Administration. It's an awesome overview of the job. It doesn't get into technologies directly, just responsibilities and concepts. I realize handing your boss a book is nuts (although I've done it), but having the reference, open in front of them, as you say, "Well, it's accepted practice that a DBA will do X because of Y" might help a little. Plus, it's a great reference.