SOAP

SOAP is a specification for exchange of structured information in a decentralized, distributed environment. As such, it represents the main way of communication between the three key actors in a service oriented architecture (SOA): service provider, service requestor and service broker. Then main goal of its design is to be simple and extensible. A SOAP message is used to request a Web service.
WebSphere Application Server V5.0.2, 5.1 and 5.1.1 follow the standards outlined in SOAP 1.1.
SOAP was submitted to the World Wide Web Consortium (W3C) as the basis of the eXtensible Markup Language (XML) Protocol Working Group by several companies, including IBM and Lotus.
SOAP is an XML-based protocol that consists of three parts: an envelope that defines a framework for describing message content and process instructions, a set of encoding rules for expressing instances of application-defined data types, and a convention for representing remote procedure calls and responses.
SOAP is transport protocol-independent and can be used in combination with a variety of protocols. In Web services that are developed and implemented for use with WebSphere Application Server, SOAP is used in combination with HyperText Transport Protocol (HTTP), HTTP extension framework, and Java Messaging Service (JMS). SOAP is also operating system independent and not tied to any programming language or component technology.
Due to these characteristics, it does not matter what technology is used to implement the client, as long as the client can issue XML messages. Similarly, the service can be implemented in any language, as long as it can process XML messages. Also, both server and client sides can reside on any suitable platform.