SproutCore runs in the browser, your production system can use whatever backend you want, as long as it sends JSON to the browser.

When I was using an early version of SproutCore to build .Mac Web Gallery last year, the backing system was a WebDAV server that produced JSON when asked. I’m pretty sure that WebObjects is the backend sending JSON to the calendar and address book applications demoed at last week’s WWDC.

The nice thing about the separation of browser logic from the backend is that you can build some static JSON fixtures you can serve from your local web server while you’re developing your application.

ETA: Charles Jolley reminds me that you can consume XML as well as JSON, but JSON remains faster.

I mean, XML is better if you have more text and fewer tags. And JSON is better if you have more tags and less text. Argh! I mean, come on, it’s that easy. But you know, there’s a big debate about it. [Steve Yegge, via Simon Wilison]

I’ve been asking that question in interviews, and I don’t think there’s still a big debate about when to use XML and when to use JSON. It’s now settled.

And Yegge’s answer is not quite right. I think the difference is between structural markup and key/value pairs.

However, there are also cases when you should prefer text/plain over JSON. A hint: every object in a Second Life sim might have an HTTP engine running in it.