>  I process documents and I don't
> typically use JAVA or other programming language to deal with them.
> As such, I prefer to have a unique identifier for versions changes.
> If not for minor changes, anything that introduces a change that
> would break backward compatibility should be identified.

It's usually better to do this with a version attribute rather than to
use a new namespace URI and thereby claim you're making a new and
entirely unrelated language.