Attention all cars. AJAX is not Web 2.0. In fact, it is in many ways in opposition to web 2.0. AJAX applications create web-pages that are less machine-readable / linkable (try bookmarking a google map). This is a mistake that I have seen some otherwise smart people making, so it’s important to clear this matter up.
Clinton agrees with me
Before we get to Web 2.0., it is useful to consider what does not characterize Web 2.0. For instance, for all of the love that rich client-side AJAX applications such as Gmail have earned, that alone does not make them Web 2.0. Simply having a Flash or WML interface or a XHTML+CSS homepage is not enough to qualify. In fact, in some cases these sites actually lock in more control over the data and manage the presentation even further.
The reason for this confusion is simple. The two memes have grown in tandem with each other in the last year. The same types of developers seem to be using both approaches, and meet at the same conferences. But correlation != causality!
Some Web 2.0 applications (like the remixed google maps/craiglist app) happen to be AJAX applications. AJAX can be a useful approach for making web applications with very rich behavior. It doesn’t have anything to do with the read/write web, which is what web 2.0 is about.
Web 2.0 is about making websites machine readable so that content can squirt seamlessly between unrelated sites. Technologies like RSS, RESTian APIs, and XHTML/CSS are the core of Web 2.0. Social networks and tagging and attention are at the core of Web 2.0. Not rich client technologies like AJAX.
If we start using “Web 2.0” to mean everything we think is cool right now, the term will quickly become meaningless and obsolete.
End of rant.