Java Web Services

Chapter 3. SOAP: The Cornerstone of Interoperability

Much like web services, the broad definition of the Simple Object Access Protocol (SOAP) means various things to different people. It’s a wire protocol. It’s an RPC mechanism. It’s an interoperability standard. It’s a document exchange protocol. It’s a universal business-to-business communications language. It’s everything you would ever need. It’s not nearly enough.

Actually, it’s all of the above. Perhaps the best way to understand what it is and what it isn’t is to break down the acronym into its parts and analyze where each one fits.

Simple

For starters, the “S” in SOAP stands for “simple.” The basic approach of expressing data as XML and transporting it across the Internet using HTTP is simple. In the SOAP protocol, everything that goes across the wire is expressed in terms of HTTP or SMTP headers, MIME encoding, and a special XML grammar for encoding application data and objects.

However, a full understanding of the details and rules of SOAP is not for the faint of heart. For instance, the idea of expressing a SOAP document with attachments using the email and MIME metaphor is simple. Is MIME simple? It is simple only because it uses a data formatting convention that is already in widespread use, is familiar to most IT people, and is conceptually understood by less technical people. Perhaps the “S” should stand for “simpler.”

Is XML simple? It can be as simple or as complex as you want it to be. XML provides a way to add ...