Chapter 11. Web Services

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Distributing functionality and data beyond the enterprise in which they were developed is the next step in component technology. Developers can integrate into their applications a much more extensive set of services than they could ever hope to develop on their own. Our Acme Reservation System case study is a simple example. The Acme Travel Agency, by using the reservation systems of the airlines and hotels, can provide a wider range of services to their clients .

One vendor will not be able to supply the necessary distributed technology infrastructure. At the very minimum, the worlds of Java, .NET, mobile computers, and legacy systems will continue. Fortunately, TCP/IP and HTTP have established themselves as industry standard networking protocols and can be the basis for any attempt to interconnect heterogeneous systems. HTTP is a text-based protocol, so using the industry standard XML to describe the interactions of these systems makes sense. Web Services use XML- and HTTP-based protocols to provide an industry standard to allow diverse systems to interconnect.

Web Services is the second part of the .NET distributed computing story. If all the applications and services that need to interconnect are all based on the Common Language Runtime, .NET remoting can be used. Its advantage is that you can remote any .NET data structure through the remoting serialization. Environments that do not run .NET, however, cannot handle the full range of .NET data types. Hence, Web Services transmit only a much more limited set of data structures that can be expressed in the XML-based protocols that Web Services use today. The versions of the SOAP protocol used by Web Services and by .NET remoting have different programming models. The latter offers full CLR fidelity. The former is constrained by interoperability standards.

Besides the ability of heterogeneous systems to interconnect, Web Services allow business partners to share information or integrate with legacy systems without having to write specialized interconnection applications. Even within a single enterprise you will be able to integrate information from internal and external sources. If Web Services are to be more than just distributed application development, however, the necessary financial, reliability, security, and legal infrastructure have to be developed.

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