Hi Developer,

From your description, you are using the MSXML component to parse a XML 
Schema file and is wondering how to select a child node from a give 
IXMLDOMNode using the selectSingleNode method, yes?

I'm not sure what version of MSXML component are you using , I've done a 
simple test via MSXML3, we can still use XPATH from the give node to select 
a certain child node under it. Here is the code of My test app:

===========main cpp file===========================
#include "stdafx.h"
#include <stdio.h>
#import <msxml3.dll>
using namespace MSXML2;



int main(int argc, char* argv[])
{
	IXMLDOMDocumentPtr pXMLDom;
   HRESULT hr;



   CoInitialize(NULL);
	
   hr = pXMLDom.CreateInstance(__uuidof(DOMDocument30));
   if (FAILED(hr)) 
   {
      printf("Failed to instantiate DOMDocument40 class\n");
      return -1;
   }


   
   pXMLDom->async = VARIANT_FALSE;
   if ( pXMLDom->load("schema.xml") != VARIANT_TRUE)
   {
      printf("Failed load xml data from file.\n%s\n",
         (LPCSTR)pXMLDom->parseError->Getreason());
      return -1;
   }

    IXMLDOMNodePtr pNode = 
pXMLDom->selectSingleNode("//xs:schema/xs:element/xs:complexType/xs:choice/x
s:element");
   pXMLDom->selectSingleNode(
   IXMLDOMNodePtr pSubNode = NULL;
   if (pNode == NULL)
   {
      printf("Invalid node fetched.\n%s\n",
         (LPCSTR)pXMLDom->parseError->Getreason());
   }
   else
   {
      printf("Result from selectSingleNode:\nNode, <%s>:\n\t%s\n\n",
         (LPCSTR)pNode->nodeName, (LPCSTR)pNode->xml);
		
	  pSubNode = 
pNode->selectSingleNode("//xs:element/xs:complexType/xs:sequence");
		
	  if (pSubNode == NULL)
	  {
		printf("Invalid node fetched.\n%s\n",
			(LPCSTR)pXMLDom->parseError->Getreason());
	  }
      else
	  {
		printf("Result from selectSingleNode:\nNode, <%s>:\n\t%s\n\n",
			(LPCSTR)pSubNode->nodeName, (LPCSTR)pNode->xml);
		
	  }

   }

   pXMLDom.Release();
   pNode.Release();
   pSubNode.Release();
   CoUninitialize();

   getchar();
   return 0;

}

============test schema file==================
<?xml version="1.0" ?>
<xs:schema id="Dataset1" targetNamespace="http://tempuri.org/Dataset1.xsd" 
xmlns:mstns="http://tempuri.org/Dataset1.xsd" 
xmlns="http://tempuri.org/Dataset1.xsd" 
xmlns:xs="http://www.w3.org/2001/XMLSchema" 
xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" 
attributeFormDefault="qualified" elementFormDefault="qualified">
  <xs:element name="Dataset1" msdata:IsDataSet="true">
    <xs:complexType>
      <xs:choice maxOccurs="unbounded">
        <xs:element name="venue_seats">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="venue_id" msdata:ReadOnly="true" 
msdata:AutoIncrement="true" type="xs:int" />
              <xs:element name="seat_id" type="xs:int" minOccurs="0" />
              <xs:element name="a" type="xs:string" minOccurs="0" />
              <xs:element name="Table1" minOccurs="0" maxOccurs="unbounded">
                <xs:complexType>
                  <xs:sequence>
                    <xs:element name="id" msdata:ReadOnly="true" 
msdata:AutoIncrement="true" type="xs:int" />
                    <xs:element name="a" type="xs:string" minOccurs="0" />
                    <xs:element name="b" type="xs:string" minOccurs="0" />
                  </xs:sequence>
                </xs:complexType>
              </xs:element>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
      </xs:choice>
    </xs:complexType>
    <xs:unique name="Dataset1Key2" msdata:PrimaryKey="true">
      <xs:selector xpath=".//mstns:Table1" />
      <xs:field xpath="mstns:id" />
    </xs:unique>
    <xs:unique name="Dataset1Key1" msdata:PrimaryKey="true">
      <xs:selector xpath=".//mstns:venue_seats" />
      <xs:field xpath="mstns:venue_id" />
    </xs:unique>
    <xs:keyref name="Table1venue_seats" refer="Dataset1Key2">
      <xs:selector xpath=".//mstns:venue_seats" />
      <xs:field xpath="mstns:seat_id" />
    </xs:keyref>
    <xs:keyref name="venue_seatsTable1" refer="Dataset1Key1" 
msdata:IsNested="true">
      <xs:selector xpath=".//mstns:Table1" />
      <xs:field xpath="mstns:id" />
    </xs:keyref>
  </xs:element>
</xs:schema>
============================================

Please have a try to see whether it helps. Thanks.

Regards,

Steven Cheng
Microsoft Online Support

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