Not that I know (haven't seen one at least), but you could generate a database schema in SQL Server management studio.
Are there any particular areas you are interested in?
Actually, there is an old one from the book Developing Solutions with EPiServer.
The book was written 2004 so it won't be up to date (think the book was released when episerver 4 was released, not sure though). It doesn't include all tables either.
But as Greger says, you should be able to generate a complete schema with Management studio.
Does anyone know if a formal document outlining the make up of the EPiServer 4.6x database schema exists.