Does anyone know of a good starting code for a Comparison tool for XML?

I'm a technical writer and we are making an update to our database management system to include an automatic change summary. When we checkout a file make changes and check the file back in, the differences between the two files will be written to a new file in a specified format.

But the issue I'm having with coding it, is I don't fully understand how Java is supposed to read H U G E XML documents.

It would need to break it down into separate files by tags (specific to the files) then compare the old vs. the new.

If anyone has any suggestions...please help...

Any yes I have Googled this...but have found nothing that would work. Maybe I'm just not searching for the right things....