Thursday, May 01, 2003

A behind the scenes look at Web Services.

A behind the scenes look at Web Services.

Web services help build distributed applications

A Web service is a software that makes itself available over the Internet and uses a standardized XML messaging system

A Web service can have a public interface, defined in a common XML grammar. The interface describes all the methods available to clients . The interface definition is accomplished via the Web Service Description Language (WSDL).

Once you create a Web service, you should be able to publish this fact. and for others to locate it This is done through UDDI, or Universal Description, Discovery, and Integration

Web services are now used for news syndication, and stock-market data to weather reports .

So what is new ?

People have been using Remote Procedure Calls (RPC) for some time now, and they long ago discovered how to send such calls over HTTP.

So, what is really new about Web services? The answer is XML.

XML lies at the core of Web services, and provides a common language for describing Remote Procedure Calls, Web services, and Web service directories.

Prior to XML, data sharing among applications was still possible, but XML makes this so much easier to do.

Through the IBM Web Services Browser, available on the IBM Alphaworks site you can access a series of Web services demonstrations. Behind the scenes, it ties together SOAP, WSDL, and UDDI to provide a simple plug-and-play interface for finding and invoking Web services. For example, you can find a stock-quote service, a traffic-report service, and a weather service. Each service is independent, and you can stack services like building blocks. You can, therefore, create a single page that displays multiple services--where the end result looks like a stripped-down version of

Web service protocol stack is an evolving set of protocols used to define, discover, and implement Web services. The core protocol stack consists of four layers:

Service Transport protocol handles transport of messages between applications. Currently, this includes HTTP, SMTP, FTP, and newer protocols, such as Blocks Extensible Exchange Protocol (BEEP).

XML Messaging protocol encodes messages in a common XML format so that messages can be understood at either end. Currently, this includes XML-RPC and SOAP.
(XML-RPC is platform independent and so diverse applications can communicate with one another. For example, a Java client can speak XML-RPC to a Perl server. SOAP focusses on Remote Procedure Calls (RPC) transported via HTTP. Like XML-RPC, SOAP is platform independent, and therefore enables diverse applications to communicate with one another.)

Service Description protocol describes the public interface to a specific Web service. Currently, service description is handled via the WSDL.Using WSDL, a client can locate a Web service, and invoke any of the publicly available functions. With WSDL-aware tools, this process can be entirely automated, enabling applications to easily integrate new services with little or no manual code

Service Discovery protocol centralizes services into a common registry, and provides easy publish/find services for Web services. This is handled via the UDDI

You do not need to understand the full protocol stack to get started with Web services. If you know the basics of HTTP, it is best to start at the XML Messaging layer and work your way up.

The Web services architecture is implemented through the layering of several types of technologies. These technologies can be organized into the following four layers that build upon one another.


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