Next Generation of Distributed Computing: Web Services

Next Generation of Distributed Computing: Web Services

An XML Web service is a programmable application component that provides some serviceable, useful functionality, such as application logic, and is available to any number of potentially incongruent systems through the use of standard protocols, such as XML and HTTP. Web services provide the ability to exchange messages in a loosely coupled environment (whereas DCOM, IIOP, and Java/RMI require tight integration between the client and the server) through the use of common data formats and standard protocols, such as XML, SOAP, and HTTP.

Since Web services are based on standard data formats and protocols, Web service applications can communicate with a wide range of implementations , platforms, and devices. As XML messaging is the fundamental means of data communication in Web services, it bridges the differences that exist between systems that use dissimilar component models, programming languages, and operating systems.

Since Web services use the underlying infrastructure provided by HTTP, Web services can move data through firewalls and between diverse systems. Therefore, we see Web services as the next generation of distributed computing. Web services are enabling a new era of distributed application development.

Benefits of Web Services

Let us see some momentous advantages of Web services.

1. Web services offer new business opportunities by making it easy to connect with partners (business-to-business integration).

2. Web services reduce application development and maintenance costs (save time and money).

3. You can create new sources of revenue by modifying the present functionality as the Web services.

4. Web services provide a solution to systems interoperability problems.

5. Web services enable crossplatform, program-to-program communications (application integration).

6. Software reuse is a time- and cost-saving benefit of Web services.

7. Web services connect information, applications, people, systems, and devices.

ASP.NET Web Services

Since ASP.NET Web services are built on top of ASP.NET, you can use the features of ASP.NET to build Web services. Distinctively, ASP.NET takes advantage of performance and security enhancements found in the .NET Framework and the CLR. Because ASP.NET is built upon the .NET Framework, ASP.NET Web services can utilize many .NET Framework features, such as authentication, caching, memory management, interoperability, and state management. Visual Studio .NET is a powerful tool for building Web applications, Web services, desktop applications, and mobile applications. The Visual Studio .NET IDE (integrated development environment) facilitates rapid application development (RAD), which enables developers to quickly create, consume , and deploy Web services. The ASP.NET and Visual Studio .NET provides an easy and simple programming model to develop and deploy Web services. For example, developers do not need to generate WSDL documents, since ASP.NET itself takes care of generating the required WSDL documents.

Web Services Architecture

The Web service infrastructure consists of the following four sections.

1. Wire Format (HTTP and SOAP)

2. Description and Discovery Stack (WSDL and Disco)

3. Directory Stack (UDDI)

4. Request/Response Service (Soap Message)

Figure E-1 shows the basic Web services architecture. Figure E-2 illustrates the four sections of the Web service infrastructure and their relationships in detail.

Figure E-1. Basic Web service architecture.

Figure E-2. Web service architecture provided by Microsoft.

Figure E-3 and Figure E-4 show the Web services interaction. The various steps involved in Web services interaction are as follows .

• The service provider, in order to publish a Web service as a one-time activity, registers the Web service definition (the WSDL) in a UDDI registry.

• The client application queries the UDDI using a description of the service it needs.

Figure E-3. Web service architecture.

Figure E-4. Web service interaction.

• If a proper Web service is found, UDDI provides a link to the WSDL document describing that Web service.

• The client uses the link to request the WSDL document for that Web service.

• The Web service returns WSDL, which describes the interface(s) for calling the Web service.

• The client makes a SOAP request, formatted according to the WSDL.

• The Web service returns a SOAP body based on the request.