I have a database and want to output a UML Diagram. Is there software that does this?
Ideally it will be UML, but a graphics representation of the database could work.
Boxes and arrows are all you need, but I'd recommend that you try E/R tools. They are similar to UML, but intended for relational databases. A good one can import and export SQL, which you won't get from a UML tool.
If you use MySQL, the MySQL Workbench does a very nice job, indeed.