• The XML Protocol Working Group is the W3C group formed in response to the submission of the SOAP 1.1 specification as the basis for a universal XML-based protocol. The formation of the Working Group signals the W3C's willingness to consider extending the Web from a network that delivers documents and links to human users, to a network that supports communication between applications.
• The goal of the XML Protocol Working Group is the creation of simple protocols that can be deployed across the Web and easily programmed through scripting languages, XML, and Web tools. It is important to note that the goal of the Working Group is not to provide a complete infrastructure for Web communication, but to build a foundational layer that can be incrementally extended to support the security, scalability, and robustness required for more complex applications.
• A key aspect of the XML Protocol Working Group is that, like all other W3C initiatives, the group effort must fit within the broader W3C goals of modularity and simplicity. In defining a protocol for the Web, it is important that the final version of the envelope and any serialization mechanisms developed by the Working Group should not preclude any programming model nor assume any particular mode of communication between peers. In addition, it should also support distributed extensibility where the communicating parties do not have a priori knowledge of each other.
• By limiting the scope of its effort to include neither transport nor application-specific features, the Working Group is better positioned to achieve its goal of producing a simple mechanism for encapsulating and representing data that is transferred between communicating peers. In keeping with the foundational W3C design principle of avoiding constraints if at all possible, the XML Protocol Working Group carries on the W3C philosophy of fostering interoperability.
• Much of the work on SOAP has been influenced by the experience of developing HTTP, which has demonstrated how difficult it is to retrofit support for evolution and how important extensibility is as a feature of an infrastructure
Taking SOAP to the Next Level
• Going beyond the simple use of SOAP to exchange data, several options are emerging that use SOAP as their base protocol.
As can be seen in Figure 4.16, other options include Electronic Business XML (ebXML) and Web services.
Although we examine ebXML and Web services in more detail in Chapter 5, it's important to realize that both these technologies impose some structure on the freewheeling world of SOAP-based communication.
As we'll see, ebXML is useful in defining messages and processes for common B2B transactions, and Web services is an infrastructure for discovering and connecting to services anywhere on the Web.
Thus rather than spending time and money defining a schema for purchase orders, a company can turn to ebXML or a Web services framework to provide a structure for communication. However, using SOAP alone is a completely satisfactory approach with minimal risk that gets the job done.
• Figure 4.16. SOAP offers an envelope for sending XML data across the Web. Technologies such as Web services and ebXML add structure and process to the B2B dialog.
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