Analysis of the Availability of Composite Web Services

Web Services become more prevalent in Internet or Intranet environments, bringing many new design challenges, due to stringent requirements such as reliability, scalability, efficiency, security, reusability, adaptability, interoperability, maintainability, availability, portability, etc. Although some of them has been gotten a lot of concerns in present research works, but the availability in composite Web service based system has not yet raised enough considerations in previous studies. This paper presents an exploratory work about this. First, we discuss the availability in Web services based system, then, a novel approach is introduced to composite Web service analysis and design for various composite patterns both from system´s and client´s perspective. It is also demonstrated that the presented approach can be used efficiently to analyze the availability of non-redundant service, part-redundant service and all-redundant service, as well as the total system. It is worth to mention that the all-redundant system obtains much better availability than non-redundant system. Therefore, to improve the availability of a system, it is necessary to provide backup service as many as possible under the consideration of tradeoff between cost and availability.