XPath and Namespace mapping

[Tahura Chaudhry]

I am new to Xalan. I have tried out the sample application "SimpleXPathAPI" 
with the command as "SimpleXPathAPI foo.xml /doc name/@last" as instructed 
in the docs. That resulted in the message:  Warning -- No nodes matched the 
location path "/doc".
When I gave the namespace prefix to the above command, i.e. "SimpleXPathAPI 
foo.xml /foo:doc foo:name/@last" it correctly displayed the output "The 
string value of the result is: Marston"

My question is if I didn'tt know ahead of time the prefix but know the 
namespace, then is there a way to construct the XPath expression. Is there a 
class which I can use to map arbitrary prefixes to namespaces and then uses 
those prefixes as path of the XPath expression. If yes, what class is this?

thanks,
Tahura