public function addTransactionHook (Db &$db)
	{
		
		// Get argument database DSN

		$dsn	= $db->getDSN ();
		
		// Set if the databases are not the same and the the database isn't already hooked
		
		if ($dsn != $this->getDSN () && !isset ($this->_transaction_hooks[$dsn]))
		{
			$this->_transaction_hooks[$dsn]	=& $db;
			return TRUE;
		}
		
		return FALSE;
		
	}