Conversation technology is not yet mature in the Web services world. While WSCL is the forerunning technology in this arena, it has not yet reached the heights of being the conversations standard.
However, WSCL is a capable, if minimal interface description language. It is based on the notion of being able to represent a conversation as a state machine, which is then itself represented in an XML form. This XML form consists of Interactions, which declare the messages exchanged between parties in a conversation and Transitions, which govern the ordering of those interactions. These are then wrapped within a Conversation element that deals with the initialization and finalization of the conversation, as well as naming, documentation, and namespace issues.
While at the time of writing there is little in the way of software support for WSCL, we have informally shown how it is relatively straightforward to automate conversational interactions with Web service technology. Furthermore, if WSCL is used simply as human-readable documentation for a Web service, then it provides an unambiguous means of specifying that service's use, which compliments and demystifies any natural language description.
However, with the advent of newer business process technologies like BPEL and WSCI (see Chapter 6), technologies like WSCL are being subsumed into the larger business process arena. While the deployment of Web service metadata in the form of WSCL interfaces is undoubtedly useful, we may yet see newer standards provide their own means of describing conversational state. It still remains to be seen whether WSCL will emerge relatively intact from the process, though one thing is for sure: we will be seeing much more of conversational interfaces in the future.