Problem in XPath

[Abhijit Das]

hi,
Is there any condition to parse a XML file by using XPath APIs?
I have a .xml file with the following heading ( it is .xpdl file generated from BPMN).

  <?xml version="1.0" encoding="utf-8"?>
 <Package xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Id="db47002c-275f-4d7e-bcba-086eccbbba0d" Name="Diagram 1" OnlyOneProcess="false" xmlns="http://www.wfmc.org/2004/XPDL2.0alpha">
<PackageHeader>
   ....
</PackageHeader>
 <....>
 ....
   ...
.....
 </...>
 
</Package>
 

The Above file is not parseing. My codeing is

  
 XPath xpath = XPathFactory.newInstance().newXPath();
            String expression = "/Package/PackageHeader";
            InputSource inputSource=new InputSource(new FileInputStream(xmlDocument));
            NodeList nodeList =  (NodeList)xpath.evaluate(expression, inputSource, XPathConstants.NODESET);
            System.out.println("Length :: " + nodeList.getLength());
            for(int i=0 ;i<nodeList.getLength(); i++){
                Node node = nodeList.item(i);
                System.out.println(":::::::::: "+i+ node);
            }
        } catch(Exception e) {
            System.out.println("Error  ::" + e.getMessage());
            e.printStackTrace();
        }
 
o/p : Length :: 0

But, once I change the attribute of <Package> elment by xmlns:journal="http://www.w3.org/2001/XMLSchema-Instance"
.

It works fine.

What is the condition for parsing with XPath APIs?

thanks