Retreive parent record values from child entity lookup

function retrieverecord() {
  if (Xrm.Page.getAttribute("childlookupid").getValue() != null) {
    //acount guid no
    var parentcustomerID = Xrm.Page.data.entity.attributes.get("childlookupid").getValue()[0].id;
    var xml = "<?xml version='1.0' encoding='utf-8'?>" +
    "<soap:Envelope xmlns:soap='http://schemas.xmlsoap.org/soap/envelope/'" +
    " xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'" +
    " xmlns:xsd='http://www.w3.org/2001/XMLSchema'>" +
    GenerateAuthenticationHeader() +
    "<soap:Body>" +
    "<Retrieve xmlns='http://schemas.microsoft.com/crm/2007/WebServices'>" +
    "<entityName>parentEntity</entityName>" +
    "<id>" + parentcustomerID + "</id>" +
    "<columnSet xmlns:q1='http://schemas.microsoft.com/crm/2006/Query' xsi:type='q1:ColumnSet'>" +
        "<q1:Attributes>" +
            "<q1:Attribute>parentattributevalue[attributenames]</q1:Attribute>" +            
        "</q1:Attributes>" +
    "</columnSet>" +
    "</Retrieve>" +
    "</soap:Body>" +
    "</soap:Envelope>";
    var xmlHttpRequest = new ActiveXObject("Msxml2.XMLHTTP");
    xmlHttpRequest.Open("POST", "/mscrmservices/2007/CrmService.asmx", false);
    xmlHttpRequest.setRequestHeader("SOAPAction", "http://schemas.microsoft.com/crm/2007/WebServices/Retrieve");
    xmlHttpRequest.setRequestHeader("Content-Type", "text/xml; charset=utf-8");
    xmlHttpRequest.setRequestHeader("Content-Length", xml.length);
    xmlHttpRequest.send(xml);
    var resultXml = xmlHttpRequest.responseXML;

    var errorCount = resultXml.selectNodes('//error').length;

    if (errorCount != 0) {
        var msg = resultXml.selectSingleNode('//description').nodeTypedValue;
        alert(msg);
    }
    //Display the retrieved value.
    else {
        alert(resultXml.selectSingleNode("//q1:parentattributevalue").nodeTypedValue);
        var cost = resultXml.selectSingleNode('//q1:parentattributevalue').nodeTypedValue;
         
       Xrm.Page.getAttribute("childattribute").setValue(parseInt(cost));
//for retreiving the option set text
//resultXml.selectSingleNode('//q1:parentattributevalue').attributes[0].text;
    }
}
}