public function toXMLString()
{
$str = '';
$str .= '<ns:DoReferenceTransactionReq>';
if ($this->DoReferenceTransactionRequest != null) {
$str .= '<ns:DoReferenceTransactionRequest>';
$str .= $this->DoReferenceTransactionRequest->toXMLString();
$str .= '</ns:DoReferenceTransactionRequest>';
}
$str .= '</ns:DoReferenceTransactionReq>';
return $str;
}