What are database variables and can you point one out on this code:

<?php

//require the PEAR:: DB classes.

require_once 'DB.php';

$db_engine = 'mysql';
$db_user = 'username';
$db_pass = 'password';
$db_host = 'localhost';
$db_name = 'database';

$datasource = $db_engine.'://'.
$db_user.':'.
$db_pass.'@'.
$db_host.'/'.
$db_name;

$db_object = DB::connect($datasource, TRUE);

/* assign database object in $db_object,

if the connection fails $db_object will contain

the error message. */

// If $db_object contains an error:

// error and exit.

if(DB::isError($db_object)) {
die($db_object->getMessage());
}

$db_object->setFetchMode(DB_FETCHMODE_ASSOC);

// we write this later on, ignore for now.

include('check_login.php');

?>