Missing Files

Files Not Found :
Creating the Model : 'app/model/a.php'

<?php
class a extends AppModel{
    public function __construct(){
        parent::__construct('a');
    }
}
?>

Creating the Controller : 'app/controller/a_controller.php'

<?php
class aController extends AppController{
	function home(){
		// home function
	}
}
?>