Web services is one of those concepts made all the more difficult to understand because of the myriad acronyms and abbreviations that pepper any conversation. The diagram below puts the most important concepts in their place: Soap/XML, UDDI and WSDL. UDDI says where services are, WSDL describes what they do and Soap talks to them. As Figure 1 shows, the process flow of a Web service is: 1. Discovery - Search UDDI site(s) for the proper Web service.
Latest Standards:
http://www.UDDI.org 2. Description - A description of the selected Web service is returned to the client application as a Web Services Description Language (WSDL) file.
Latest Standards:
http://www.w3.org/2002/ws/desc/ 3. Proxy creation - A local proxy to the remote service is created.
Latest Standards:
There are no standards associated with a proxy, apart from the Soap/XML message that it creates (see below). The proxy converts an object's means of method invocation into an XML message, and vice versa. 4. Soap Message Creation - a Soap/XML message is created and sent to the URL specified in the WSDL file.
Latest Standards:
http://www.w3.org/
http://www.ws-i.org 5. Listener - A Soap listener at the host site receives the call and interprets it for the Web Service. 6. The Web service performs its function, and returns the result back to the client, via the listener and the proxy. Of course to achieve this utopia of Web services talking to each other, the technologies have to be there and work together properly. On the next page, we explain just how far they have each come -- and much farther they have to go.