As the number of Web services increases and groups of competing Web services that provide the same or similar capability emerge, quality of service (QoS) becomes an important differentiating feature that directly drives a Web service's usefulness and popularity. Exposing a piece of business logic as a Web service is not difficult; architecting the service so that it meets the quality needs of its users and also maintains that level of quality over a sustained period of time is the difficult part.
In this chapter, we took a tour of quality of service as it relates to Web services. We touched on some of the QoS measures that are critical for enterprise applications. We discussed the technologies that underlie Web services as well as related systems and how these technologies and systems contribute positively or negatively to QoS metrics. We then took an in-depth look at architectural and design patterns as well as best practices for developing QoS-enabled Web services and client applications.