Ajax isn't a technology. It's really several technologies, each flourishing in its own right, coming together in powerful new ways. Ajax incorporates:         * standards-_base_d presentation using XHTML and CSS;         * dynamic display and interaction using the Document _object_ Model;         * data interchange and manipulation using _xml_ and XSLT;         * asynchronous data retrieval using _xml_HttpRequest;         * and _java_script__ binding everything together. Web 2.0 Design Patterns In his book, A Pattern Language, Christopher Alexander prescribes a format for the concise de_script_ion of the solution to architectural problems. He writes: Each pattern describes a problem that occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.    1. The Long Tail       Small sites make up the bulk of the internet's content; narrow niches make up the bulk of internet's the possible applications. Therefore: Leverage customer-self service and algorithmic data management to reach out to the entire web, to the edges and not just the center, to the long tail and not just the head.    2. Data is the Next Intel Inside       Applications are increasingly data-driven. Therefore: For competitive advantage, seek to own a unique, hard-to-recreate source of data.    3. Users Add Value       The key to competitive advantage in internet applications is the extent to which users add their own data to that which you provide. Therefore: Don't restrict your architecture of participation to software development. Involve your users both implicitly and explicitly in adding value to your application.    4. Network Effects by Default       Only a small percentage of users will go to the trouble of adding value to your application. Therefore: Set inclusive defaults for aggregating user data as a side-effect of their use of the application.    5. Some Rights Reserved. Intellectual property protection limits re-use and prevents experimentation. Therefore: When benefits come from collective adoption, not private restriction, make sure that barriers to adoption are low. Follow existing standards, and use licenses with as few restrictions as possible. Design for hackability and remixability.    6. The Perpetual Beta       When devices and programs are connected to the internet, applications are no longer software artifacts, they are ongoing services. Therefore: Don't package up new features into monolithic releases, but instead add them on a regular basis as part of the normal user experience. Engage your users as real-time testers, and instrument the service so that you know how people use the new features.    7. Cooperate, Don't Control       Web 2.0 applications are built of a network of cooperating data services. Therefore: Offer web services interfaces and content syndication, and re-use the data services of others. Support lightweight programming models that allow for loosely-coupled systems.    8. Software Above the Level of a Single Device       The PC is no longer the only access device for internet applications, and applications that are limited to a single device are less valuable than those that are connected. Therefore: Design your application from the get-go to integrate services across handheld devices, PCs, and internet servers. AJAX is also a key component of Web 2.0 applications such as Flickr, now part of Yahoo!, 37signals' applications _base_camp and backpack, as well as other Google applications such as Gmail and Orkut. We're entering an unprecedented period of user interface innovation, as web developers are finally able to build web applications as rich as local PC-_base_d applications. Interestingly, many of the capabilities now being explored have been around for many years. In the late '90s, both Microsoft and Netscape had a vision of the kind of capabilities that are now finally being realized, but their battle over the standards to be used made cross-browser applications difficult. It was only when Microsoft definitively won the browser wars, and there was a single de-facto browser standard to write to, that this kind of application became possible. And while Firefox has reintroduced competition to the browser market, at least so far we haven't seen the destructive competition over web standards that held back progress in the '90s. We expect to see many new web applications over the next few years, both truly novel applications, and rich web reimplementations of PC applications. Every platform change to date has also created opportunities for a leadership change in the dominant applications of the previous platform. Gmail has already provided some interesting innovations in email, combining the strengths of the web (accessible from anywhere, deep data_base_ competencies, searchability) with user interfaces that approach PC interfaces in usability. Meanwhile, other mail clients on the PC platform are nibbling away at the problem from the other end, adding IM and presence capabilities. How far are we from an integrated communications client combining the best of email, IM, and the cell phone, using VoIP to add voice capabilities to the rich capabilities of web applications? The race is on. It's easy to see how Web 2.0 will also remake the address book. A Web 2.0-_style_ address book would treat the local address book on the PC or phone merely as a cache of the contacts you've explicitly asked the system to remember. Meanwhile, a web-_base_d synchronization agent, Gmail-_style_, would remember every message sent or received, every email address and every phone number used, and build social networking heuristics to decide which ones to offer up as alternatives when an answer wasn't found in the local cache. Lacking an answer there, the system would query the broader social network. A Web 2.0 word processor would support wiki-_style_ collaborative editing, not just standalone documents. But it would also support the rich formatting we've come to expect in PC-_base_d word processors. Writely is a good example of such an application, although it hasn't yet gained wide traction. Nor will the Web 2.0 revolution be limited to PC applications. Salesforce.com demonstrates how the web can be used to deliver software as a service, in enterprise scale applications such as CRM. The competitive opportunity for new entrants is to fully embrace the potential of Web 2.0. Companies that succeed will create applications that learn from their users, using an architecture of participation to build a commanding advantage not just in the software interface, but in the richness of the shared data. Core Competencies of Web 2.0 Companies In exploring the seven principles above, we've highlighted some of the principal features of Web 2.0. Each of the examples we've explored demonstrates one or more of those key principles, but may miss others. Let's close, therefore, by summarizing what we believe to be the core competencies of Web 2.0 companies:     * Services, not packaged software, with cost-effective scalability     * Control over unique, hard-to-recreate data sources that get richer as more people use them     * Trusting users as co-developers     * Harnessing collective intelligence     * Leveraging the long tail through customer self-service     * Software above the level of a single device     * Lightweight user interfaces, development models, AND business models The next time a company claims that it's Web 2.0, test their features against the list above. The more points they score, the more they are worthy of the name. Remember, though, that excellence in one area may be more telling than some small steps in all seven. Tim O'Reilly O'Reilly Media, Inc., This e-mail address is being protected from spam bots, you need JavaScript enabled to view it President and CEO _link_: http://www.oreillynet.com/pub/a/oreilly/tim/news/2005/09/30/what-is-w...