PHP - Having Some Problems With A Few Classes I Wrote

Hi all. I have a singleton database class that just basically extends PDO. I then created a file called configure.php that will be included on every single page in my small application. In this file, I get the database instance and also instantiate a Site class that returns information about the site, pages, etc. Well, for some reason my Site class is not reading the $database variable that is defined in the configure.php file. I am getting the following error: "Notice: Undefined variable: database in C:\xampp\htdocs\individualbasic\libraries\Site.php on line 30

Fatal error: Call to a member function prepare() on a non-object in C:\xampp\htdocs\individualbasic\libraries\Site.php on line 30". Below are my files. Thanks in advance.

Database.php
Code: [Select]
<?php
class Database extends PDO
{

public static $_instance;

public function __construct() {
try {
parent::__construct(DB_TYPE . ':host=' . DB_HOST . ';dbname=' . DB_NAME, DB_USER, DB_PASS);
} catch (PDOException $e) {
$this->error = $e->getMessage();
}
}

public static function getInstance() {
if (!self::$_instance) {
self::$_instance = new Database();
}
return self::$_instance;
}

public function __destruct() {
// I want to close the connection here.
}

}

Site.php
Code: [Select]
<?php
class Site
{

/**
 * Checks the validity of the site token with the token in the MinorCorp database.
 */
public function __construct() {
/*try {
$query = $database->prepare("SELECT individual_site_url, individual_site_token 
FROM individual_site 
WHERE individual_site_url = ? 
AND individual_site_token = ? 
AND individual_site_active = 1");
$result = $query->execute(array(SITE_URL, SITE_TOKEN));
if (count($result) == 1) {
return TRUE;
}
die('Your website is not valid.');
} catch (Exception $e) {
echo $e;
}*/
}

/**
 * Retrieves vital information about each page.
 */
public function page($page) {
try {
$query = $database->prepare("SELECT page_title, page_keywords, page_description, page_content, page_image 
FROM page 
WHERE page_name = ?");
$query->execute(array($page));
return $query->fetch();
} catch (Exception $e) {
echo $e;
}
}

/**
 * Retrieves bottom advertisements from the MinorCorp database.
 */
public function bannerAd() {
try {

} catch (Exception $e) {
echo $e;
}
}

/**
 * Retrieves vital information about each page.
 */
public function sidebarAd() {
try {

} catch (Exception $e) {
echo $e;
}
}
}

configure.php (This is the file that is included on every page)
Code: [Select]
<?php
include_once('configuration/configuration.php');

require_once('libraries/Database.php');
$database = Database::getInstance();

require_once('libraries/Site.php');
$site = new Site();

$pageInfo = $site->page($page);
$bottomAd = $site->bannerAd();
$sidebarAd = $site->sidebarAd();