Enter Web Services

Despite the usual drawbacks of emerging technology, Web services at least the notion of Web services is an interesting technology for the world of inter- and intracompany application integration. Web services hold the promise of moving beyond the simple exchange of information the dominating mechanism for application integration today to the concept of accessing application services that are encapsulated within old and new applications. This means organizations can not only move information from application to application, they can also create composite applications, leveraging any number of back-end application services found in any number of applications, local or remote. This is the idea behind SOAI.

Key to this concept is figuring out how Web services fit into the existing application integration technology and approaches. For example, when is the use of Web services appropriate and how is cost-effectiveness determined? Keep in mind that implementing Web services is bound to be an invasive process, and thus more expensive than enabling systems for simple information exchange. We'll cover some of the basics here, and then explore more about Web services later in this book, including specific standards and technologies.

Web Services by Example

So, now that we know what Web services are, how do we use them in practice? Say we have a very good application that we build to calculate tariffs on goods coming into the United States, and we would like to allow others outside of our company to access this service using Web services (perhaps for a fee).

To accomplish this we must do the following:

First, change the application so it knows how to expose itself as a Web service; for example, it is able to respond to a SOAP request.

Second, create and send the WSDL to those applications that would like to invoke this service (perhaps send the WSDL to UDDI for more of a global reach).

Finally, the client applications should be able to invoke the server application and execute the service as if it was local to the calling applications functionally equivalent to an RPC.

After this infrastructure is set up the tariff application service is exposed to the calling applications and accessible as if it were local to the application.