Representation of classes included in the UML diagram

Hello!

I am currently testing the possibilities of using UML representation of a class.
In my class, I have included another class.
-----------------------------
class test extends tools{

     protected $_aaa = null;

     public function __construct ($_aaa)
     {
         $this->_aaa = $_aaa;
     }

     public function bla(){
        $database = new database();
     }
}

class tools{

     public function toolBlub(){

     }

     public function toolbla(){

     }
}

class database{

    public function connectDatabase(){

    }

}
-----------------------------

Why this class in the UML diagram is not displayed?

Your sincerly

Stephan