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Protocol-Based Integration
Application integration is simplified when message-based protocols are used for all communication. By building a self-contained system for description and messaging that is independent of programming language or operating system details, Web services have shown that it is possible for applications running in truly disparate environments to communicate securely and reliably. The only way this could be made to work was to assume no shared OS, virtual machine, programming language or abstraction. Independence from underlying implementation technology is the key to Web services interoperability. Web services have influenced many aspects of software development. The primary contribution of Web services has been the emphasis on protocol-based software integration. The influence of protocol-based integration on the industry at large can be seen in the increasing emphasis on service-oriented architectures.Web services have used many concepts from prior software development approaches. Both Web services and service orientation owe much to the ideas of component software, distributed objects, and message-oriented middleware. Information encapsulation and polymorphism have been adopted from object orientation, and mandatory use of interfaces and the use of run-time metadata have been adopted from component software. Distributed objects contributed notions of context that flows among entities and broker-based bindings. Of course, message-oriented middleware brought the use of queues, relays and explicit message passing.Web services communicate using a concrete set of protocols based on a common architecture with SOAP as its foundation. In contrast, service orientation is an abstract set of ideas and concepts that can be manifested in any number of ways (much like object orientation before it).Web services can be used to implement a service-oriented system, but service orientation does not necessitate the use of Web service protocols, nor does the use of Web service protocols ensure that the overall system design is service-oriented. As a technology, Web services enable the easy interconnection of services into rich solutions. To facilitate the development of Web servicesbased solutions, Microsoft is investing heavily in making the combination of Web services and service orientation an important part of Microsoft Windows.The broad adoption of Web services is accelerating as a result of several underlying factors. First, network infrastructure is now pervasiveenabling cost-effective computer to computer communication. Second, systems built from services provide a software development approach that enables legacy applications to be incorporated in incremental steps. Third, systems developed with autonomous services acknowledge the reality of today's computing environment, where independent but collaborating businesses work together to provide common solutions. Finally, service autonomy provides for more robust applications given the reduction in coupling, the use of explicit contracts, and the ability to upgrade participant services independently.This introduction has presented the main enablers, motivators, requirements, and principles that guide the Web services architecture. The rest of this book presents the core technologies that underlie the architecture, followed by a tour through the collection of specifications that define the Web services architecture.
