PHP:如何处理 SOAP 响应以获取标记值?

I've a SOAP response in a var $soap_response like this:

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:clr="http://schemas.microsoft.com/soap/encoding/clr/1.0">
   <SOAP-ENV:Header>
      <h3:__MethodSignature xsi:type="SOAP-ENC:methodSignature" SOAP-ENC:root="1" xmlns:h3="http://schemas.microsoft.com/clr/soap/messageProperties" xmlns:a2="http://schemas.microsoft.com/clr/ns/System.Collections">xsd:string a2:Hashtable</h3:__MethodSignature>
   </SOAP-ENV:Header>
   <SOAP-ENV:Body>
      <i4:ReturnDataSetResponse id="ref-1" xmlns:i4="http://schemas.microsoft.com/clr/nsassem/TOIServerAppl.clsRSchedule/TOIServerAppl">
         <return href="#ref-6"/>
      </i4:ReturnDataSetResponse>
      <a3:DataSet id="ref-6" xmlns:a3="http://schemas.microsoft.com/clr/nsassem/System.Data/System.Data%2C%20Version%3D1.0.5000.0%2C%20Culture%3Dneutral%2C%20PublicKeyToken%3Db77a5c561934e089">
         <XmlSchema id="ref-7"><![CDATA[<?xml version="1.0" encoding="utf-16"?>
            <xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
              <xs:element name="NewDataSet" msdata:IsDataSet="true">
                <xs:complexType>
                  <xs:choice maxOccurs="unbounded">
                    <xs:element name="Table">
                      <xs:complexType>
                        <xs:sequence>
                          <xs:element name="id" type="xs:long" msdata:targetNamespace="" minOccurs="0" />
                        </xs:sequence>
                      </xs:complexType>
                    </xs:element>
                  </xs:choice>
                </xs:complexType>
              </xs:element>
            </xs:schema>]]>
        </XmlSchema>
        <XmlDiffGram id="ref-8">
            <id>4437031</id>
        </XmlDiffGram>
      </a3:DataSet>
   </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

如何从 4437031 中提取 id 值?

simplexml_load_string($soap_response);