A service-oriented architecture isn't much more than a loosely coupled collection of services - often Web services. Services are defined as a unit of work done by a service provider for a service consumer. One of the ways that SOA achieves that loose coupling is by remaining independent of a given technology (such as PHP or ColdFusion) and hiding the details of the implementation - much like a Web service.
Figure 6.8 illustrates a very basic SOA. The Service Consumer makes a request to the Service Provider and the Service Provider sends a response. Since the response is often in XML, AJAX is a nearly ideal tool for designing a lightweight browser-based client for a SOA. AJAX provides a dynamic interface that can provide an experience reminiscent of a desktop application at a fraction of the cost and significantly less hardware.
