private function fromArrayToXmlString(array $array)
    {
        $string = '';

        foreach ($array as $key => $value) {
            $string .= '<' . $key . '>' .
                ((is_array($value))
                    ? $this->fromArrayToXmlString($value)
                    : $value) .
                '</' . $key . '>';
        }

        return $string;
    }