The dbx module is a database abstraction layer (db 'X', where 'X' is a supported database). The dbx functions allow you to access all supported databases using a single calling convention. The dbx-functions themselves do not interface directly to the databases, but interface to the modules that are used to support these databases.
Note: This extension has been moved to the » PECL repository and is no longer bundled with PHP as of PHP 5.1.0.