The Web's business and technology elite convened for O'Reilly and Associates' third annual Web 2.0 Conference in San Francisco's Palace Hotel last week. Started in 2004, the meeting lends its name to what some call a movement and others an ignorable wave of marketing hype.

What is Web 2.0? The concept is notoriously fluid, and easy to apply to whatever topic, site or idea that the speaker wants to show off. Tim O'Reilly's own definition includes a three-color diagram with 20-odd boxes and lines. The easiest definition, however, is simply the group of new Web sites that have grown after the dot-com crash at the turn of the millennium. The most interesting and important of these show four key properties: an emphasis on social software, exposing useful web services, a culture of openness, and a rich browser interface.

Is Web 2.0 relevant for open source developers, users, and IT managers? Although it may seem like just so much marketing fluff, Web 2.0 does have meaning for open source creators and users as well as IT decision-makers.

Opensourciness

Web 2.0 sites exhibit, to steal a trick from Steven Colbert, "Opensourciness". Some of the most successful sites, like del.icio.us and digg.com, are an outgrowth of open source culture. Most sites began as personal projects to "scratch an itch" for developers and friends, or as small start-ups run on a tight budget. This has engendered a close interaction between developer and audience, and a consequent release early, release often responsiveness in the development of new features.

The start-up culture of Web 2.0, with more restricted post-crash budgets, has led to an even more pronounced dependence on open source software -- either a Linux Apache MySQL PHP/Perl/Python (LAMP) stack or increasingly popular alternatives including Lighttpd and Ruby -- than in the pre-crash Web. More importantly, as Web 2.0 sites have grown up into serious businesses, few have migrated away from the rapid-development high-level languages to "serious" development platforms.

Web 2.0 sites like the photo-sharing service Flickr encourage hacking of third-party tools, providing APIs and open-format data for plugins, extensions, and other experimentation by users. Some companies are even encouraging a purely API-based system, such as Amazon's interesting pay-to-play Web services. Some sites, such as WordPad, LiveJournal, and Wikipedia, release their software under a free license, encouraging the kind of improvements that feed back into their core sites.

One of the most notable features of many Web 2.0 sites, is the emergence of Asynchronous JavaScript and XML (AJAX) interfaces -- JavaScript-based dynamic sites that modify HTML and use micro-requests to the server. Most Web 2.0 sites incorporate some AJAX interactivity; some, such as meebo.com, make it the core of their interface. While JavaScript interfaces were once anathema, their re-emergence is directly attributable to the rise of Mozilla and Firefox, and to a lesser extent Konqueror and Safari, and the consequent viability of standards-based Web development. Thanks to these open source browsers, Web developers have been able to depend on richer interaction in their browser interfaces.

Most importantly, many Web 2.0 sites extend open source values into non-programmatic objects: images, video, text. Many, but by no means all, Web 2.0 sites support an open management culture, such as the one defined by Jonathan Nolen's Open Company Test. The Creative Commons suite of licenses, released in 2001, have been used extensively in blogging services such as Blogger and photo-sharing services such as Flickr. Although many sites support a "spectrum" of licenses -- from the most restrictive to the most liberal, and everything in between -- large content wikis such as Wikipedia make all their text and images available under free licenses. Together these services are making a huge corpus of work available for free use.