July 25, 2002
Web Service Discovery techniques. Doug
Web Service Discovery techniques. Doug Tidwell. Al Gore said in 1984 that "applications will be based on compositions of services discovered ... dynamically".
Web Service example: MagicEightBall. Advantage of Web Services is that you can take existing stuff and put it out on the web. Use Apache Axis and deploy class as Web service. In order to use the service, the client needs to know:: the address of the machine, the id of the service, the name of the methods, the parameters to a method, the contents of the SOAPAction field. SOAP toolkits do most of the work for you. But how do you discover what you need? WSDL, WSIL, UDDI.
WSDL: W3C, supported by Axis, WSDL2Java, Java2WSDL, "?WSDL" to generate WSDL from the service. But we still need to discover the WSDL file.
WSIL and UDDI: Web Services Inspection Language and Universal Description, Discovery and Integration protocol. With WSIL - I know the host I want to work with. I go to the host and get a list of services (inspection.wsil). Like index.html. With UDDI I do not know the host and therefore it is more difficult. A UDDI server is a SOAP server in itself. Metadata about services can be stored in the registry. The UDDI spec calls this concept: "technical models" or "tModels". Question from the floor: What about contracts and SLAs? Why do I then need UDDI? Answer: These things are being worked on. But because of this most UDDI is inside a firewall.
Right way to discover a service: Search in a trusted registry for a service, choose the provider based on criteria, invoke the service. But not feasable outside an institution..
Posted by Matthew at July 25, 2002 07:46 PM