public static function isAccessibleBy($document, $user)
    {
        $result = null;
        switch (Convertor::baseClassName($user)) {
            case 'User': //Admin
                $result = true;
                break;
            case 'Customer': //Customer
                $result = (self::getDocumentCompany($document) == self::getCustomerCompany($user));
                break;
            case 'Anonym': //Anonymous
                $result = false;
                break;
        }
        return $result;
    }