Once the mainframe and non-mainframe transactions can be treated as XML components, it becomes surprisingly simple to provide a number of useful services. Just the browser interface alone reduces user errors and new user learning time. The composite application approach is very powerful, and can provide significantly improved workflow for the users. Perhaps most interestingly, composite applications are not limited to a single application, nor to a single host.

At the start of the article, we asked what are Web Services good for today, before all this future, pie in the sky prognostication proves itself true (or false)? How will it help get the work done that has to get done, every day? The answer is Enterprise Application Integration (EAI), one of the most rapidly growing areas of work within the enterprise today. We believe that Web Services will dramatically reduce the cost of application integration in the enterprise, and will replace expensive, proprietary EAI solutions with inexpensive commoditized solutions based on open standards.

The earliest attempts at application integration involved allowing query access to enterprise data for anyone who could justify it. This solution was really just a stopgap, and it created new problems as it solved old ones. Allowing direct access to enterprise data required all users, many of whom might be unsophisticated computer users, to learn and correctly replicate existing business rules in order to issue a correct query. And, allowing update access was simply too dangerous in almost all circumstances.

Web Services are defined as transactions, so that proven business rules mediate all access to and update of data stores. Once the transactions are defined as Web Services, then anyone with appropriate access within the enterprise can discover and consume any needed service without fear of compromising system integrity, including the updates hitherto prohibited.

This is a great deal more than simply providing universal browser access to enterprise applications, although that is certainly one use. It is also more than re-engineering the user interface to reduce the number of steps required to accomplish a task, as we touched on briefly in the discussion of super-functions above.

Web Services immediately open up the possibility of easily assembling composite applications from multiple applications on different hosts, in which we combine existing functions in novel ways, or we create new functionality freely intermixed with old. This is the most important aspect of Web Services today. All existing transactions become Web components that can be used as building blocks for new applications.