How to extract value using php soapclient

I have just started learning to program with PHP SOAPclient. I have the following xml file and I want to extract/get the value rs-1开发者_运维问答304338811289-11595:

 <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Body>
        <ns2:deliverMDRecordsResponse xmlns:ns2="http://mdstore.data.dnetlib.eu/" xmlns:ns3="http://www.w3.org/2005/08/addressing">
         <return>
             <ns3:Address>http://129.70.212.20:8282/dnet-mdstore/service/MDStoreResultSet</ns3:Address>
             <ns3:ReferenceParameters>
                 <ResourceIdentifier:ResourceIdentifierxmlns:ResourceIdentifier="http://www.driver.org" xmlns:wsa="http://www.w3.org/2005/08/addressing">rs-1304338811289-11595</ResourceIdentifier:ResourceIdentifier>
          </ns3:ReferenceParameters>
-......
         </return>
     </ns2:deliverMDRecordsResponse>
    </soap:Body>
  </soap:Envelope>

    <?php
    $source = 'resourceIdentifier.xml';

    $xml = simplexml_load_string($source);
    $xml->registerXPathNamespace('identifier', 'ns3');
    foreach ($xml->xpath('//identifier:ResourceIdentifier') as $item)
    {
        print_r($item);

    }

    ?>

Your simplexml namespace registration statement is broken:

Try this:

    <?
    $source=<<<END
        <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
      <soap:Body>
      <ns2:deliverMDRecordsResponse xmlns:ns2="http://mdstore.data.dnetlib.eu/" xmlns:ns3="http://www.w3.org/2005/08/addressing">
             <return>
      <ns3:Address>http://129.70.212.20:8282/dnet-mdstore/service/MDStoreResultSet</ns3:Address>
      <ns3:ReferenceParameters>
      <ResourceIdentifier:ResourceIdentifier xmlns:ResourceIdentifier="http://www.driver.org" xmlns:wsa="http://www.w3.org/2005/08/addressing">r\
    s-1304338811289-11595</ResourceIdentifier:ResourceIdentifier>
      </ns3:ReferenceParameters>
             </return>
      </ns2:deliverMDRecordsResponse>
      </soap:Body>
      </soap:Envelope>
    END;
    $xml = simplexml_load_string($source);
    $xml->registerXPathNamespace('t', 'http://www.driver.org');
    foreach ($xml->xpath('//t:ResourceIdentifier') as $item)
    {
      //  print_r($item);
      echo $item->asXML();
    }
?>