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Chapter 1. Introduction to the Web Services Architecture
The Web has been a phenomenal success at enabling simple human/computer interactions at Internet scale. The original HTTP [HTTP] an110 [HTML] protocol stack used by today's Web browsers has proven to be a cost-effective way to project user interfaces onto a wide array of devices. A key factor in the success of HTTP an110 in achieving broad adoption was their relative simplicityboth HTTP an110 are primarily text-based and can be implemented using a variety of operating systems and programming environments.Web services take many of the ideas and principles of the Web and apply them to computer/computer interactions. Like the World Wide Web, Web services communicate using a set of foundation protocols that share a common architecture and are meant to be realized in a variety of independently developed and deployed systems. Like the World Wide Web, Web services protocols owe much to the text-based heritage of the Internet and are designed to layer as cleanly as possible without undue dependencies within the protocol stack.An important area in which Web services differ from the World Wide Web is scope. HTTP an110 were designed around "read-mostly" interactive browsing of content that is often static, or at least highly cacheable. In contrast, the Web services architecture is designed to also support highly dynamic program-to-program interactions. The communicating programs can be co-located at a computer or distributed across a network. In the Web services architecture, many kinds of distributed systems can be implemented. Examples include synchronous and asynchronous messaging systems, distributed computational clusters, mobile networked systems, grid systems, and peer-to-peer environments. The broad spectrum of requirements in program-to-program interactions forces the Web services protocol stack to be much more general-purpose than the first Web protocols. However, like the Web, Web services rely on a small number of specific protocols. We'll discuss these at more length later.We envision that the next generation of mainstream applications will be based on autonomous Web services. These services may be provided by multiple organizations and may span any number of geographic or organizational boundaries. As a result, these applications cannot assume the existence of central authorities, nor is mutual trust between services to be expected. The implications of autonomy are central to the architecture, and they will be explored throughout this book. The technical content of this book describes the infrastructure protocols defining the Web services architecture and a key concept needed to build autonomous distributed applications: the concept of contracts.The core principles that have driven the design and implementation of the Web services architecture protocols are as follows:Message orientation Using only messages to communicate between services and realizing that messages often have a life beyond a given transmission event.Protocol composability Avoiding monoliths through the use of infrastructure protocol building blocks that can be used in nearly any combination.Autonomous services Allowing endpoints to be independently built, deployed, managed, versioned, and secured.Managed transparency Controlling which aspects of an endpoint are (and are not) visible to external services.Protocol-based integration Restricting cross-application coupling to wire artifacts only.
The remainder of this section describes these principles in detail.
