Perhaps the single most important factor that sets Web services apart from previous distributed systems frameworks is not interoperability as we might at first think (since if vendors were enthusiastic enough they could have made prior systems interoperate), but extensibility. In contrast to previous systems like CORBA, where the message format and content were closely tied together each bit in a message field was fixed and had significance for some a priori determined protocol SOAP is modular and arbitrarily extensible for new protocols. This extensibility has been exemplified in this chapter. We have seen disparate enterprise requirements like transactions and security implemented in such a way that they are both independent of one-another and yet can operate seamlessly side-by-side in the same application, even without having to alter any application code.
As more and more enterprise processes are automated and made electronic, the need for 24 hours by 7 days-a-week access to these automated environments becomes increasingly important. Mobile devices such as personal digital assistants and Internet-capable cellular phones present a good platform for providing such pervasive access. We have shown how mobilizing an existing enterprise Web services-based application can be simplified by using a proxy-based architecture. A few simple changes to the existing application together with a mobile client application and a mobile proxy that intermediates between the mobile client and the back-end application is all that is needed. Development and testing times are minimized, thus reducing time-to-market and costs.
Of course, while Web services solve a number of problems for architects and developers, they do not necessarily solve any problems for the business user directly, since they are a system development aid and not a business tool. However, we are already seeing Web services becoming encapsulated behind "business analyst-friendly" APIs with efforts like BPEL (and its tool support) abstracting away much of the detail of the underlying Web services-based infrastructure and presenting the user with a business-focused view of the problem domain.
It is finally becoming clear that enterprise-level quality of service can be implemented in a Web services environment, though the implementations are necessarily less advanced than the equivalent software designed for proprietary systems. This will improve as the whole industry moves its focus to Web services.