II SOA and WS * Extensions

One thing we learned in Part I of this book is that, though simple in concept, SOA in real life can quickly become a complex entity. Looking back at all of the characteristics we associated with contemporary SOA, we now need to roll up our sleeves and start figuring out exactly how we are going to go about realizing them.

A good place to start is by continuing our exploration of the Web services framework into the world of second-generation Web services specificationsor WS-*. The most interesting and perhaps unnerving part of the contemporary SOA landscape is this ever-evolving family of Web services specifications. As we discussed in Chapter 4, there are different paths along which these documents can make their way into the IT mainstream. And, as with any form of evolution, some survive, and some don't.

Over the next two chapters we delve into detailed concepts introduced by a key collection of WS-* extensions. The majority of the specifications covered are relatively established. Some emerging specifications are also discussed to provide a glimpse of what's on the horizon.

The extensions or features offered by WS-* specifications have not only duplicated some of the traditional features associated with enterprise computing, they have also built upon and extended the fundamentals of service-orientation. As much as these extensions are enabling vendors to broaden the Web services-based feature-set of their proprietary platforms, they are also responsible for expanding the technology landscape that comprises SOA.

Sections covering concepts derived from WS-* specifications are ended with a study of how these extensions support a subset of the primitive and contemporary SOA characteristics we identified in Chapter 3.

Specifically, we look at the following:

• loose coupling
• composability
• interoperability
• reusability
• extensibility
• vendor diversity
• discoverability
• quality of service

How contemporary SOA characteristics are further supported by WS-* extensions and other SOA influences is explored in Chapter 9. Note also that considering our focus in this part of the book remains the conceptual side of SOA, we do not explain the language or syntax behind the specifications themselves. (Language details are covered in subsequent chapters.)

What is WS * ?

The term "WS-*" has become a commonly used abbreviation that refers to the second-generation Web services specifications. These are extensions to the basic Web services framework established by first-generation standards represented by WSDL, SOAP, and UDDI. The term "WS-*" became popular because the majority of titles given to second-generation Web services specifications have been prefixed with "WS-". (See www.specifications.ws for examples of WS-* specifications.)