Programming Visual Basic .NET

Web-Service Discovery

Up to this point, we have assumed that the client of a web service knows where to find that web service’s WSDL document. This may not always be the case. For example, consider a client application that runs on a portable device. Its purpose is to make a reservation on the user’s behalf at the nearest hotel meeting the user’s preset price and service guidelines. Before the client application can communicate with a hotel’s reservation web service, the client must have a way to discover that the service is even there. This is the purpose of web-service directories.

Web-service directories provide a way for clients to find web services that perform a certain task or a certain kind of task. They are like the yellow pages in a telephone directory, in which businesses are listed according to the product or service they provide. Standards are just now being developed for web-service directories. One strong contender is called Universal Description, Discovery, and Integration (UDDI). Information about this standard and the implementations that currently exist can be found at http://www.uddi.org.

You may also have heard of DISCO files. (DISCO is short for discovery.) DISCO is a Microsoft-exclusive specification for encoding the addresses of multiple WSDL documents into a single XML document. DISCO doesn’t have directory capabilities and so is falling into disuse as UDDI grows.