Abstract
With the widespread use of the Internet, the number of web services that can provide similar functionality has increased rapidly in recent years. Web service selection has to be based on some non-functional attributes of the services, such as the quality of service (QoS). In this chapter, we use a server switching service that is commonly used in Internet hosting environments to explain how an agent can use a performance model to evaluate services and select the most suitable services among a number of functionally similar services returned by the service discovery. The various criteria that can be used to assess QoS are introduced in this chapter, including mean response time, throughput, system utilisation and others closely related to business such as revenue and operating costs. Service selection in the chosen case study depends on the quality and suitability of various switching policies, in other words, different switching policies can be selected depending on the QoS of the services and the run-time system state. Since the system performance can be evaluated using an analytic model, therefore, the QoS of services is assessed based on the output of the performance model.