The legacy of Web 1.0 will be felt for years to come. In fact, the vast majority of traffic on the Internet still follows this paradigm. You have an endless number of sites, large and small, that still present their view of the world in a tightly controlled environment — managed explicitly at all times between the client and the server. For example, if you shop at Expedia or Travelocity you will be able to buy plane tickets, but you will do so reading their content, using their interface, using their shopping cart, all on their web site.

Thus Web 1.0 was the enabling of the small individual to present itself on par with a much larger entity.

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.

There is an intermediary stage in between Web 1.0 and Web 2.0. Chronologically, of course, nothing is that linear — patterns sometimes arrive early, sometimes far before the world is ready for them. There is a tremendous amount of overlap in each of these phases, and nothing is dying off completely.

Web 1.5 was an early tremor that signaled that data, all data, wanted to break free of the tightly controlled environments of before. Web 1.5 was the birth of the web service API. Amazon’s Web Services are one of the earliest examples of a large scale web services API with meaningful data. Other major sites followed suit — EBay, Yahoo!, Google, have all exposed web services that enable people to access the underlying data without being cornered into one particular application of that data. But this alone is not Web 2.0, though it is a very important step in that direction.

Web 2.0 is about giving up control. It is about setting the data free. It is about providing services that work with other people’s data. It is about having a valuable resource and making no presumptions about how or where that resource will be used.

There are two traits that characterize Web 2.0 and differentiate it from Web 1.5. First, Web 2.0 APIs tend to be symmetrical and reciprocal in the sense that not only can data be read out via published interfaces, but can it also be written into those interfaces. This is most apparent when the API is REST-based and supports the full HTTP method set of GET, HEAD, POST, PUT, etc. SOAP APIs can also qualify, and the Web Service Description Language (WSDL) is a necessary component for the discovery of such interfaces. Second, Web 2.0 APIs are open standards with formal semantic meaning. This, more than anything else, differentiates the applications of Web 2.0 from those that came before. For example, the Amazon Web Services APIs are incredibly rich, but in order to use them a client application must be specifically aware of the AWS protocols and formats. Similarly, in order to use Google Maps, a client application must know specifically about, and code specifically to, the Google API.

Where Web 1.5 is about exposing the data, Web 2.0 is about giving that data meaning and thereby setting it free.

Web 2.0 is the syndication of data, and syndicating it in such a way that anyone, anywhere can use the results. Web 2.0 does not lock the consumer (who also becomes a producer) into rigid use cases — it intentionally forfeits that control in favor of much greater returns. And Web 2.0 adds semantic meaning to the data so that the interconnected network of consumers and producers can evolve and adapt and thrive as the system grows. And importantly, Web 2.0 is about symmetrical and reciprocal relationships between producers and consumers to the point where the lines become blurred and one becomes the other.

In a sense, Web 3.0 will be more of the same. This incremental stage will be characterized by our ability to stream media in real-time — similar to the way that Web 2.0 lets us syndicate much simpler data today. Convergence will extend to include streaming video and audio over interoperable channels.

Your handheld mobile device will call the same media APIs that your flat-panel plasma display does.

If Web 2.0 is about the convergence of text and semantic data, Web 3.0 will do the same for all digital media.

And to go really out on a limb — what will Web 10.0 be? Most likely, even more along those lines. Imagine a scenario in which any data — all data — can be instantaneously streamed anywhere at anytime. Your very experiences, your senses, perhaps even your thoughts, will be broadcast and archived for anyone to download and view. All human knowledge will be publicly accessible — all music, all art, all media, all things. The distinction between human thought and computer thought will be blurred. We will be part of the network, the network will be part of us. We will be the hive mind, and we collectively will have evolved into something quite unlike anything the world has ever seen.