Research On Several Key Problems Of Web Service Reliability

With the wide use of web services technologies, the QoS of web services receives more and more concerns. As an important attribute of QoS, reliability is one of the most important criteria employed by users to select appropriate services. However, while its significance is self-evident, up to now the research on the reliability of web service is still in an elementary stage and many problems remain to be answered. Under such a circumstance, this paper tries to address some key issues on web service reliability.Currently, there is still no common understanding of what web service reliability is and how it should be measured. After analyzing the problems of existing definitions given by former researchers, this paper presents a descriptive definition of web service reliability. In addition, a method is proposed to quantify the service reliability from the consumers'perspective.After the discussion of defining and quantifying the reliability of service, this paper proposes a user feedback based reliability evaluation model. In the current web services publish-find-bind model, service consumers have no sources to obtain the reliability information of services. After close analysis of three possible sources of web service reliability information, a model is designed to help consumers acquire the information provided by former consumers.It's a basic requirement for web service composer to predict or assess the reliability of a composite web service before it's published. Unlike traditional product-oriented software, usually it's not an appropriate approach to evaluate the reliability of a composite web service by using group testing methods. Inspired by the block diagram reduction procedures, the papers gives seven rules to reduce the web service workflow graph and compute the reliability of equivalent service.Finally, this paper gives a close examination of the applicability of software fault-tolerant methods for web services and proves that both N-version programming and recovery block scheme can improve the reliability of a composite web service effectively.