• Introduction
  SOAP is an XML-based object invocation protocol. SOAP was originally developed for distributed applications to communicate over HTTP and through corporate firewalls. SOAP defines the use of XML and HTTP to access services, objects and servers in a platform-independent manner. SOAP provides a way to access services, objects, and servers in a completely platform-independent manner.
  
  Read Sample Chapters from books on SOAP.
  
  SOAP is a wire protocol that can be used to facilitate highly ultra-distributed architecture.
  
  SOAP is simple. It is nothing more and nothing less than a protocol that defines how to access services, objects, and servers in a platform-independent manner using HTTP and XML.
  
  Don Box says "One protocol that will undoubtedly have a profound effect on the world of software engineering is Simple Object Access Protocol, or SOAP for short", also "SOAP is a protocol that allows method calls to be made across the Web using XML. We wanted to fix DCOM."
  
  From the W3C Web site:

  SOAP Version 1.2 is a lightweight protocol intended for exchanging structured information in a decentralized, distributed environment. "Part 0: Primer" is a non-normative document intended to provide an easily understandable tutorial on the features of the SOAP Version 1.2 specifications "Part 1: Messaging Framework" defines, using XML technologies, an extensible messaging framework containing a message construct that can be exchanged over a variety of underlying protocols. "Part 2: Adjuncts" defines a set of adjuncts that may be used with SOAP Version 1.2 Part1: Messaging Framework.

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  Also see: A nice short article about history of SOAP
  Don Box takes a look back at the last three years of SOAP. A nice reading!
  
  Book excerpt (SOAP: Cross Platform Web Service Development Using XML [by Scott Seely]):
  An XML Overview Towards Understanding SOAP
  
  Yet another nice introductory article: Simply SOAP



• Web Services (SOAP) Interoperability links
• Understanding Web service interoperability


• WS-I: an open, industry organization chartered to promote Web services interoperability


• Apache SOAP Toolkit: Interoperability with Other SOAP Implementations


• Web Services Interoperability and SOAP


• SOAP Builders Mailing List


• Microsoft SOAP Interop Server


• SOAPBuilders Interoperability Lab (XMethods.net)


• SOAPBuilders Interoperability Lab "Round 2" (whitemesa.com)


• Apache SOAP 2.2 with MSTK 2.0 clients using WSDL


• Testing for SOAP Interoperability: Locating and Testing