XML and Java: Developing Web Applications, Second Edition

12.4 Summary

In this chapter, we have discussed XML messaging. First we showed the XML messaging stack to give an overview of XML messaging. The messaging stack defines the following three layers:

• Application

• Messaging

• Transport

In addition, we provided a distinction between RPC and document-centric messaging, emphasizing the importance of both.

We also discussed SOAP, addressing some important concepts such as the Envelope, header processing, the intermediary, and SOAP encoding. We also developed a prototype SOAP engine to understand how easy it is to develop a SOAP engine. As product-level SOAP engines, we described Apache SOAP and Axis. We believe that experience with the prototype can help you better understand the products.

XML messaging is expected to play a central role in future B2B collaborations. Especially, SOAP is considered a key technology because it has been widely accepted, and therefore interoperability can be achieved to some extent. On the other hand, a number of problems must be solved for real business use. At the least, support for security and transactions is mandatory. As we discuss in Chap ter 14, security for XML and SOAP is proceeding well. An XML digital signature has been submitted to W3C and recently became a Recommendation. On the other hand, there is no active standardization for transactions, but you should keep your eyes on it.

In Chapter 13, we extend our perspective from XML messaging to Web services. As we will show there, you should know three basic technologies for Web services: SOAP, Web Services Description Language (WSDL), and Universal Description, Discovery, and Integration (UDDI). We have already explained one of them, and applications accessible via SOAP are Web services by definition. When we explain the other two technologies, you will see the big picture of Web services.