使用PHP读取WSDL文件的对象数组

我不熟悉Web服务。我需要使用PHPSOAPClient函数从SOAP响应中读取发票对象数组。下面是我的SOAP响应：

<Soap:Envelope xmlns:Soap="http://schemas.xmlsoap.org/soap/envelope/">
   <Soap:Body>
      <InvoiceQuery_Result xmlns="urn:web">
         <xmlInvoice>
            <Header xmlns="urn:Invoice">
               <Cust_No>12345</Cust_No>               
               <Lines>
                  <Line_No>10000</Line_No>                  
                  <LotSerial>
                     <Qty>1</Qty>
                     <Serial>12345-001</Serial>
                  </LotSerial>
               </Lines>               
            </Header>
            <Header xmlns="urn:Invoice">
               <Cust_No>12346</Cust_No>               
               <Lines>
                  <Line_No>10001</Line_No>                  
                  <LotSerial>
                     <Qty>2</Qty>
                     <Serial>12345-002</Serial>
                  </LotSerial>
               </Lines>               
            </Header>
            <Header xmlns="urn:Invoice">
               <Cust_No>12347</Cust_No>               
               <Lines>
                  <Line_No>10002</Line_No>                  
                  <LotSerial>
                     <Qty>4</Qty>
                     <Serial>12345-003</Serial>
                  </LotSerial>
               </Lines>               
            </Header>
         </xmlInvoice>
      </InvoiceQuery_Result>
   </Soap:Body>
</Soap:Envelope>

12345
10000
1.
12345-001
12346
10001
2.
12345-002
12347
10002
4.
12345-003

问题是什么？