WEB SERVICES DEFINED

We all understand the need to continually seek opportunities to improve operational efficiencies, perhaps through better communications or through closer collaboration with partners and suppliers. These pressures, combined with the emergence of open standards, have created an environment in which Web services are poised to become the platform of choice for future application integration projects. Web services deliver the basic building blocks that enable the World Wide Web to evolve to a new level. The Web will no longer be the sole domain of the solitary “Web surfer” flitting from Web page to Web page. Increasingly, we will see the Web being leveraged as a key business tool where computer systems will exchange information with each other via Web services. Early adopters are already are using Web services to reduce the cost of internal system integration. Moreover, a few leading-edge organizations are already taking the first tentative steps toward implementing Web services that operate across the Web, as with the example of D&B’s Global Access Toolkit.

Looking beyond the early adoption of Web services for integration and collaboration, it is likely that Web services will have a significant influence on the way in which computer systems are developed and deployed. Similar to the paradigm shift of the early 1990s with the move from monolithic mainframe systems to client-server systems, today we see the start of a new paradigm shift from client-server and distributed systems to serviceoriented systems, implemented using Web services. As illustrated in Figure 2.1, the migration from the monolithic systems of the 1970s, through client-server and distributed systems toward service-oriented systems, has progressively seen the following trends:

Figure 2.1: Shift to service orientation.

• A Migration to Loosely Coupled Systems —The mainframe systems of the 1970s were implemented as large blocks of functionality that ran on a single mainframe computer. In contrast, service-oriented systems are implemented as discrete business services that are loosely coupled to other services running of a mix of hardware and software platforms across the organization.

• Greater Adaptability and Flexibility —Early mainframe systems used paper tape and punch cards to store data and programs. The use of mainframe processing time was strictly managed and allocated in sequential blocks or batches. In contrast, service-oriented systems (implemented as discrete business services) are interconnected across an organization’s computer network, where it is possible to locate and reuse services registered with a central registry or “yellow pages” of services.

Unlike previous architectural paradigms, the move to Web services will not necessitate a “rip ‘n’ replace” approach. Rather, Web services will encapsulate existing systems and expose functionality as reusable services using Web services standards.

Service-oriented system development, and more specifically Web services, leverage five key principles that, when considered together, define and differentiate Web services from previous application implementation paradigms. The five key principles maintain that Web services are:

1. Loosely Coupled —One of the key advantages of Web services is that loosely coupled systems are more flexible and more easily reconfigured—enabling components of a system to be replaced or exchanged with relative ease.

2. Self-Describing —The Web Services Description Language (WSDL) is an XML document that describes a Web service’s inputs and outputs in a structured manner. The WSDL document enables other software to determine how to invoke the service and determine what results the service will return.

3. Accessed Programmatically —Web services do not have a Graphical User Interface (GUI) because they are not designed to be accessed directly through human interaction. Instead, they are invoked by and exchange data with other software applications programmatically using the Simple Object Access Protocol (SOAP).This programmatic access enables a Web service to be incorporated into other software applications, Web sites, or even other Web services.

4. Network Distributed —Web services are accessed using Internet protocols and data formats such as TCP/IP, HTTP, and XML. Using these existing protocols and data formats, Web services comply with current company security measures and policies (for example, corporate firewalls). This feature makes it possible for Web services to be deployed and accessed across corporate intranets or the Internet.

5. Exchange Data Using Vendor, Platform and Language-Neutral Protocols —This capability is perhaps the most important and compelling aspect of Web services. The ability for a Web service to exchange data in a vendor, platform and language-neutral format is facilitated through broad industry agreement on open standards.

These five defining principles can be combined into a succinct definition-of a Web service:

“Web Services are loosely coupled, self-describing services that are accessed programmatically across a distributed network, and exchange data using vendor, platform, and language-neutral protocols.”

Fundamentally, the key principles of Web services are enabled by agreement on standards across a broad group of hardware and software organizations. The following sections examine the standards that form the foundation upon which Web services are implemented and discuss why the continued agreement on standards is so important to the realization of business benefit from Web services.