SOAP and the RequestResponse Model

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The SOAP standard introduces no new concepts—it's built completely from existing technology. It currently uses HTTP as its request/response messaging transport and is completely platform independent. As you know, HTTP connects computers across the entire world. HTTP can go through firewalls and is the easiest means to transport messages to any computer in the world. It's likely that SOAP will evolve to use other protocols in the future.

A SOAP package contains information that can be used to invoke a method. How that method is called is not defined in the SOAP specification. SOAP also does not handle distributed garbage collection, message boxcarring,² type safety, or bidirectional HTTP. What SOAP does allow you to do is pass parameters and commands between HTTP clients and servers, regardless of the platforms and applications on the client and server. The parameters and commands are encoded using XML. Let's take a look at how SOAP uses the standard HTTP headers.