This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
What do you mean by "explains"? Do you have some particular question about comparing two XML files? There are a LOT of products that compare two XML files, which the Google search I suggested would return. Are you not interested in any of those?