From Online Manual
Description: Name of the database being used. Such as MySQL, PostgreSQL and SQlite. Shall not be called as a function, but used a string.
Return: A string with the name of the DBMS in use. It can return MySQL, PostgreSQL or SQlite.
$versions['db_server'] = array('title' => sprintf($txt['support_versions_db'], $smcFunc['db_title']), 'version' => '');