XML Doc ref to XML Doc

Hello XML Group,
                           Iam a student, Mahi, doing Thesis work.
My requirement:

Shortly::
             I need to refer an ID of an element from one XML Document to another XML Document. Is this possible or not? Iam trying to use XPointer. But I couldnt understand its function properly. Is XPointer is the way to do so.

Eagerly waiting for your reply which help me as a clue in my Thesis.

Best Regards,
Mahi