An XML-based conversational protocol for web services

SOAP is used to communicate with Web services. It defines the a messaging framework (the envelope), encoding rules and a binding protocol over the HTTP protocol. However SOAP, as it is, does not deal with conversations. To provide full interoperability, clients need to not only know the correct data formats to pass, but also the conversation level protocol involving those messages for any required Web service. This must also include the valid responses, where multiple responses are possible, and the starting and ending states of the conversation.This paper describes an XML-based conversational protocol for Web services. Each server site publishes details enabling client agents to interact with the server. This involves the publication of protocol specifications representing a finite state machine (FSM). A client agent downloads this specification, validate it for correctness, and then implement the protocol dynamically, as a state machine. This can be viewed as a negotiation of protocols where the client negotiates to implement all requirements of a server.