August 2001 marked the tenth anniversary of the start of the Web revolution, which was launched with the release of the first publicly available software for building Web sites. In the decade since that introduction, standards-based Web communications have emerged as the dominant computing paradigm and what might be called the "third wave" of computing--replacing the proprietary client-server model, which in turn had displaced mainframes and dumb terminals.

Now the enterprise is poised at the edge of a fourth wave: message-based computing. Ten years from now, we will likely look back on the first decade of the new millennium as the period when Web-based computing moved to the next level. But how will this new wave of computing affect the enterprise? And what are the key standards and business drivers behind it?

Certainly, message-based computing must uphold the values afforded by the Web, such as permanent accessibility and true openness. Vendors must "open up" their technology to offer customers real freedom of choice.

In 1994, Gartner Group spelled out what most companies already knew: that building and maintaining client-server applications were much more expensive than the raw software and hardware costs might suggest. Gartner's calculations of the total cost of ownership of client-server applications led to a revolution in the way companies viewed the return on investment from IT and helped accelerate the uptake of Web-style working based on simple, universal standards and ubiquitous connections. Yet something was still missing.

The third wave of computing included a major shift from proprietary network protocols to standard Web protocols, but much of the rest of the client-server model remains. Browsers can query many hundreds of different servers, but they must still "pull" information down to the user at regular intervals by querying servers for data. Contrast this with media such as radio and television, where users select channels and have the information "pushed" to them.

In effect, a browser client is like a phone that doesn't ring--only servers are able to take the equivalent of incoming calls. While this simple arrangement has provided a powerful foundation for the initial Web revolution, it has come with a set of limitations. These limitations are what provides much of the inspiration behind message-based computing.

The media currently offers many examples of message-based computing models: peer-to-peer architectures, the real-time interconnection of business systems within corporations, streaming and content distribution networks, to name a few. In all these examples, the computers in the system can both initiate and receive communication "phone calls." This facility is enabling a whole range of new applications and business opportunities, allowing applications to communicate in real-time as well as dramatically reducing the costs of integrating and maintaining disparate applications.