SOAP is the communications protocol for web services. It defines the format for web services messages. SOAP Encoding is used to tell the SOAP runtime environment how to translate from data structures, such as Java, into SOAP XML. SOAP and the WSDL dictate the communication between web services and their clients.

A SOAP message contains the following sections:

Authentication and transaction management are typical examples of extensions that can be implemented as header entries. The SOAP header helps to process the data in the body of the SOAP message. Information related to authentication or transactions is usually contained in the header because this information identifies the entity that sent the SOAP message body and the context in which it will be processed.

Use a SOAP toolkit to create and parse SOAP messages. A SOAP toolkit translates function calls from another language to a SOAP message. For example, the Apache Axis toolkit translates Java function calls to SOAP.

Use SOAP to implement web services on different platforms both inside and outside an organization. Each SOAP implementation supports different function calls and parameters. Therefore, a function that works with one toolkit may not work with another.