The install procedure has a selection for the database to use at the install.
For now the choice is limited to only MySQL.
But the install procedure is not using the database factory for calling the generic database functions, but calls the mysql functions directly. Eg page_dbconnection uses mysql_connect in stead of connect.
The selection of the database is set by a config.php. This should be automatic by scanning the directory for the presence of database drivers as eg mysqldatabase.php, mssqldatabase.php, etc.