Section 4.4. Differences Between SOAP 1.1 and 1.2

4.4. Differences Between SOAP 1.1 and 1.2

The SOAP 1.2 Recommendation and SOAP 1.1 are different in a couple of ways. The W3C working group has spent most of its time clarifying and componentizing SOAP. The SOAP 1.1 specification contained a processing model, HTTP binding, a pattern for remote procedure calls (RPCs), and encoding all within the same specification. This might have led implementers to believe that SOAP was intended only for interacting with services over HTTP using RPC. That is why the working group decided to restructure and extend the specification into a set of documents that underline the flexibility of SOAP and its usefulness for different use cases.

The resulting SOAP 1.2 Recommendation consists of three documents. The first, Part 0, is a primer that reviews the complete SOAP Recommendation, including the support for attachments. The second document, Part 1, describes the core SOAP specification as a messaging framework. Part 1 describes the SOAP message in terms of the XML Infoset, together with its associated processing model. The use of the XML Infoset in describing the SOAP message allows the message structure to be documented without referring to its serialization. The messaging framework also describes SOAP's extensibility with a framework that allows SOAP bindings to be described to different underlying network protocols.

The third document, Part 2, contains the remainder of the specification as a set of optional features. This includes a description of a data model and encoding mechanism in addition to patterns for SOAP's use for RPC. The document then describes mechanisms for extending SOAP with further features and a framework for binding to network protocols. The core SOAP specification describes a one-way message, which is why the third part also includes descriptions of how to combine the one-way message into more complex message exchange patterns, such as request/reply. Finally, Part 2 includes a binding to HTTP as an example of a request/reply pattern.

This restructuring emphasizes the flexibility of SOAP and is intended to solve the perceived restrictions of the SOAP 1.1 specifications. For a detailed listing of the differences between SOAP 1.1 and 1.2, review section 6 of the SOAP 1.2 primer [SOAP 1.2 Part 0].