XrX is a combination of technologies I’ve been working with for a few years now:

X(Forms)- r(EST)-X(Query)

In short this translates to XForms, which transmits XML data from HTML POST forms, via REST (read: HTTP), to an XQuery engine or database, like MarkLogic.

It is extremely powerful. Unfortunately the first X, XForms, is not yet well supported on most browsers. I believe FireFox is the only one that has any kind of wide support for it, and even that is not fully up to the spec yet.

Why is it important? In my view, XrX will be the next wave of web development. Using these technologies, one can reduce the technology stack required to power a web application (and if you don’t believe web apps are the future, NOW, you’re still living in the last decade) from four (HTML/CSS/Javascript/AJAX, JSP, J2EE, Database) down to one.

Yes, ONE. I’ve written whole webapps using XrX (Okay, just the rX part since XForms wasn’t working well) using MarkLogic. I can just as easily do it with eXist DB, which is a product I’d really like to look at in detail.

How is this possible? XQuery, courtesy of the same W3C folks who brought you XML, is a very powerful language that lets one express everything declaratively in terms of your XML structure. Using an XML database, which generally comes with some form of HTTP server, one can thus serve HTML/CSS/Javascript content out of that database, using XQuery and XML to store the required parts.

And staying all in one language on the backend, as much as possible, vastly reduces the development time.