XML language for database schema definitions

Hello I am developing a PHP-implemented library which would allow a PHP programmer to write pre-defined data to a database. The library would be able to work with different database schemas and I need a way to "inform" the library with what kind of database schema it has to work with. I thought a good way to do that would be to describe the database schemas in XML. Because I don't want to write a new DTD just for this application, do you have any idea whether a database schema definition DTD already exists which allows XML documents to describe how a database is structured? -- NSK http://portal.wikinerds.org