how to compare part of xml to a part of another xml? [duplicate]

Possible Duplicate:

Best way to compare 2 XML documents in Java

in java, I have 2 xml files, with different root elements. I know that a part of the first onbe equals to a part of the second one. what is the best way to compare?

thanks.

I would suggest to try with XMLUnit - http://xmlunit.sourceforge.net/