本书的内容涵盖了Web Services的各种关键技术、Web Services的整体体系架构和应用体系架构，以及Web Services应用的设计和开发。本书以Web Services技术系列为主线，逐一详细分析解释包括Web Services的各种核心技术，包括XML, Namespace, XML Schema, SOAP, WSDL, UDDI, WS-Inspection, WS-Security, WS-Routing等。在分析阐述的同时，使用了大量的应用设计案例和基于Microsoft.NET的开发实例，以使读者能够更形象地理解这些技术与技术的设计思路、设计原则和相应的实现方法。
　　本书适用于对计算机技术的基础和架构已经有了一定的了解，对Web应用的架构有一定了解，同时又对当今正在发生的计算机技术的新一代技术与应用革命--Web Services浪潮的本质有着浓厚的兴趣的读者。

Preface
Web services have taken a dramatic step forward over the past year. We are quickly moving through the transition from the introduction of a compelling new architecture to deploying Web services solutions that provide significant customer value. In building these solutions, developers are being provided with the wave of updated tools and other supporting resources they need to be as productive as possible. Most importantly, the industry specifications that are available have rapidly expanded beyond the basics of SOAP, WSDL and UDDI, and into areas supporting much more sophisticated requirements. Finally, focused industry efforts to provide practical developer guidance, such as the Web Services-Interoperability Organization, have emerged to complete the picture and work across industry standards organizations.

Roadmap and Architecture

Along with the fast evolution of specifications and technologies, so has our view of the Web services architecture. As basic Web services concepts were introduced, many developers took early steps to develop solutions with relatively simple message patterns and requirements. These were the 'Stock Ticker' and 'Weather Report' services that became our latest version of 'hello, world'. With that experience behind us, it is now clear that a much richer set of protocols are required to develop the next wave of distributed systems. Industry leaders, such as Microsoft and IBM, have already stepped up to meet these needs. The latest Web services specifications fall into a few key areas - with others still in progress.

First, security requirements are being addressed through the WS-Security specification. While this is a very lightweight specification, it provides the key elements needed to carry security tokens, sign, and encrypt SOAP messages in a consistent way. More work remains, but this necessary foundation allows us to expand beyond simply transport security for Web services, and we now have a framework for much richer security features.

Next, support for distributed transactions has been introduced through the WS-Coordination and WS-Transaction specifications. These protocols allow us to develop much more sophisticated Web services solutions, but also require us to look at our Web services applications from a different perspective. Activities can now be coordinated across multiple Web services, instead of each being completely independent..

Finally, the release of the Business Process Execution Language for Web services (BPEL4WS) allows us to match our Web services with our business process and workflow requirements.

These latest specifications provide the next layer of functionality we need to build distributed systems with Web services. More work remains to expand capabilities around security and to address reliable messaging. As we continue to evolve our Web services implementations, we should consider the implications of having these rich protocols readily available as a part of our development tools and environment.

The Interoperability Imperative

While the suite of Web services specifications has expanded dramatically, their parallel development has introduced challenges in interoperability. The pace of development has, in some areas, resulted in ambiguities or redundancy. Also, many of the core specifications are general purpose, and can be applied beyond the scope of Web services. The result is variation in how developers use the specifications in their Web services, and a lack of interoperability between implementations.

Fortunately, the industry has already identified this challenge and taken proactive steps to address it. The solution is the new Web Services-Interoperability Organization (WS-I). WS-I is a consortium of vendors and customers working together to provide developers with the resources and guidance they need to develop interoperable Web services. The organization not only provides guidance, but also sample code and testing tools for developers to implement their Web services the right way.

Future Expectations

As we continue to expand our Web services solutions, we should do so with the expectation that the protocols we have available to us will become increasingly sophisticated. In many ways, limitations we encounter today can be viewed as temporary. As developers get to the business of coding their Web services, incorporating the work of WS-I helps ensure that the requirements around interoperability are met.

Christopher Kurt
Secretariat and Founding Board Member, Web Services-Interoperability Organization
Group Program Manager - Web Services Standards, Microsoft Corporation