Web Services Essentials

SOAP Encoding

SOAP includes a built-in set of rules for encoding data types. This enables the SOAP message to indicate specific data types, such as integers, floats, doubles, or arrays. Most of the time, the encoding rules are implemented directly by the SOAP toolkit you choose, and are therefore hidden from you. It is nonetheless useful to understand the basics of SOAP encoding, particularly if you are intercepting SOAP messages and trying to debug an application. Note also that while the W3C specification encourages the use of SOAP encoding rules, these rules are not required; this enables you to choose a different encoding schema, should the need arise.

When exploring the SOAP encoding rules, it is important to note that the XML 1.0 specification does not include rules for encoding data types. The original SOAP specification therefore had to define its own data encoding rules. Subsequent to early drafts of the SOAP specification, the W3C released the XML Schema specification. The XML Schema Part 2: Datatypes specification provides a standard framework for encoding data types within XML documents. The SOAP specification therefore adopted the XML Schema conventions. However, even though the latest SOAP specification adopts all the built-in types defined by XML Schema, it still maintains its own convention for defining constructs not standardized by XML Schema, such as arrays and references. Arrays are discussed in detail in the Section 3.3.2 section, later in this chapter.