The Concept of 'Real-Time' on the Web

My first job out of college was a computer engineering gig, programming in C on an OS/2 platform (yikes!). But the real key characteristic that made things interesting was the fact that the application consisted of a real-time monitoring piece - temperatures within a hot steel casting machine were updated once per second (not the fastest 'real-time', but still...) and monitored for patterns which would indicate trouble with a capital 'T'.

Fast forward 15 years or so (man, I'm feeling old now), and the meme of a 'real-time web' is now making the rounds. There are some inherent challenges with this concept - mainly due to the fact that HTTP is the basis of most of the web's transactions, and HTTP is clearly a request/response protocol. So the big challenge these days seems to be this: how do we effectively and efficiently get real-time updates or notifications via this platform?

RSS was a precursor to the eventual solution, I think. RSS allows a web application to effectively 'monitor' changes on any other web application (yes, that is what it boils down to in a programmatic sense), and that is a good start. But it kind of falls apart when you scale it up by an order of magnitude.

XMPP seems like the next good attempt at a 'real-time web' technology, and I'm keeping my eye on it as it develops...until someone comes up with the next big solution, at least.