Web Services Technologies

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	XML, Web Services, and the Data Revolution By Frank  P.  Coyle
	Table of Contents
	Chapter 5.   Web Services

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An architecture built around a client, a provider, and a registry .

Web services depends on several enabling technologies including XML, SOAP, UDDI, and WSDL. In the following sections we examine UDDI and WSDL, key pieces in the Web services framework.

The Web Services Architecture

As Figure 5.2 illustrates, there are three major aspects to Web services:

• A service provider provides an interface for software that can carry out a specified set of tasks .

• A service requester discovers and invokes a software service to provide a business solution. The requester will commonly invoke a remote procedure call on the service provider, passing parameter data to the provider and receiving a result in reply.

• A repository or broker manages and publishes the service. Service providers publish their services with the broker, and requests access those services by creating bindings to the service provider.

Figure 5.2. The Web services triad includes a broker, a service provider, and a service requester.

Key Technologies

Web services builds on SOAP, UDDI, and WSDL.

Web services relies on several key underlying technologies, in particular, UDDI, WSDL, and SOAP.

UDDI is a protocol for describing Web services components that allows businesses to register with an Internet directory so they can advertise their services and companies can find each other and carry out transactions over the Web.

WSDL is the proposed standard for describing a Web service. WSDL is built around an XML-based service Interface Definition Language that defines both the service interface and the implementation details. WSDL details may be obtained from UDDI entries that describe the SOAP messages needed to use a particular Web service.

SOAP is a protocol for communicating with a UDDI service (see Figure 5.3). SOAP simplifies UDDI access by allowing applications to invoke object methods or functions residing on remote servers. The advantage of SOAP is that it can use universal HTTP to make a request and to receive a response. SOAP requests and responses use XML not only to target the remote method but to package any data that is required by the method.

Figure 5.3. Communication involving UDDI uses SOAP to package UDDI requests and replies to a Web services repository.

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