Programming Web Services with Perl

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 5

CHAPTER 5

Introduction to SOAP

The Simple Object Access Protocol (SOAP) is the basis for the W3C design for web

services. The specifications that make up SOAP cover the expression of data, what to

require for communication, and how to link messages with communication layers.

When using toolkits (introduced in Chapter 6), it is often not necessary to know

more than just the basic elements of SOAP. But the more thorough your understand-

ing, the easier you can develop better, more efficient applications.

This chapter introduces the basic parts of SOAP, and illustrates how they work

together to create a platform for distributed application development. The focus of

this chapter is the XML that implements SOAP requests and responses and how the

SOAP specification is built from other XML technologies, such as XML Schema. Later

chapters build SOAP-enabled applications with toolkits, but to make full use of the

toolkits, you must know the constraints of the SOAP protocol that they implement.

Background

Where CORBA and COM+ followed RPC, SOAP and XML-RPC are more like its

contemporaries. While SOAP was going through a very thorough process of require-

ments gathering and design analysis, XML-RPC was spun off from an early draft of

SOAP.

The time spent in design and planning was far from squandered. The resulting speci-

fication from the working group is very flexible and leaves a considerable amount of

room for expansion of the protocol. Expansion and extension of the protocol may

come from added XML applications bundled into the encoding layer, in either (or

both) of the message header and body. Beyond this, the protocol itself is kept by ver-

sion and maintained as a W3C Technical Recommendation, the term used by the

W3C for standards that have been adopted.

At the time of this writing, the Technical Recommendation (TR) of the specification

is at Version 1.1, with Version 1.2 currently very close to acceptance as the new cur-