GDataXMLDocument nodesForXPath return an error - iphone

Question

I need your help, i want to parse an XML file using GDataXMLDocument and i want to fetch particular tag's all attributes but when i am using or just provide me the XPath's value to get columnHeading value
GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:[NSData dataWithContentsOfFile:path] encoding:NSUTF8StringEncoding error:NULL];
NSArray *tempArray = [doc nodesForXPath:#"//root/xsd:schema" namespaces:nil error:nil];
it returns below error.
XPath error : Undefined namespace prefix
xmlXPathEval: evaluation failed
And here is my XML content.
<?xml version="1.0" encoding="utf-8"?>
<SH xmlns="urn:schemas-microsoft-com:xml-analysis:rowset">
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:saw-sql="urn:saw-sql" targetNamespace="urn:schemas-microsoft-com:xml-analysis:rowset">
<xsd:complexType name="R">
<xsd:sequence>
<xsd:element name="S0" saw-sql:columnHeading="SID" saw-sql:columnID="0"/>
<xsd:element name="S1" saw-sql:columnHeading="SNAME" saw-sql:columnID="1"/>
<xsd:element name="S2" saw-sql:columnHeading="CLASS" saw-sql:columnID="2"/>
<xsd:element name="S3" saw-sql:columnHeading="ADD" saw-sql:columnID="3"/>
<xsd:element name="S4" saw-sql:columnHeading="CITY" saw-sql:columnID="4"/>
</xsd:sequence>
</xsd:complexType>
</xsd:schema>
Stuck here from last 3 days. need your help.
Thanks in advance.

Answer 1

Finally i got the solution related to my question... and here is the answer for that.
GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:[NSData dataWithContentsOfFile:path] encoding:NSUTF8StringEncoding error:NULL];
NSDictionary *myNS = [NSDictionary dictionaryWithObjectsAndKeys:
#"urn:schemas-microsoft-com:xml-analysis:rowset", #"xmlns",
#"http://www.w3.org/2001/XMLSchema", #"xsd",
#"urn:saw-sql",#"saw-sql", nil];
NSArray *tempArray = [doc nodesForXPath:#"//xmlns:RS/xsd:schema/xsd:complexType/xsd:sequence/xsd:element" namespaces:myNS error:nil];
NSMutableArray *keyArray = [[NSMutableArray alloc]initWithCapacity:0];
for(GDataXMLElement *columns in tempArray)
{
GDataXMLNode *xmlElement = [columns attributeForName:#"saw-sql:columnHeading"];
// GDataXMLNode* xmlElement = [[[element2 elementsForName:#"xsd:element"]objectAtIndex:0]attributeForName:#"saw-sql:columnHeading"];
[keyArray addObject:xmlElement.stringValue];
// NSLog(#"%#",xmlElement.stringValue);
}