基于发布/订阅机制的Web服务QoS信息分发模型

A Publish/Subscribe Based Information Dissemination Model for QoS of Web Services

QoS感知的Web服务管理和组合的基本问题是如何及时有效地获取Web服务的QoS信息.当前的研究包括基于查询或监视的方法.然而在动态的服务计算环境下,这些方法或多或少存在时效慢、代价高和可扩展性差等问题.提出一个基于发布/订阅机制的Web服务QoS信息分发模型,目标是提供一个在大规模的服务计算环境下可靠、及时地获得Web服务QoS信息的方法.提出一个基于P2P的内容发布/订阅网络,利用专用的集合点和副本机制减少订阅丢失,改善可靠性.利用RP链加快订阅和QoS信息发布.通过支持组合服务的组合QoS订阅,减少通知消息数量,减轻网络负载.仿真实验验证了系统的低成本、有效性和可扩展性.

Quality of service （QoS） information for Web services is essential to QoS-aware service management. Currently, most work assumes that the overall QoS of a composite service can be computed by the pre-existing QoS information of component services. However, the issue of how to obtain these QoS information has largely been overlooked. Current research on this problem usually involves query-based or monitoring-based methods. However, in a dynamic service oriented computing （SOC） environment, these solutions suffer from some or all of the limitations, such as cost, timeliness guarantee and scalability. In this paper, a P2P based publish/subscribe model is proposed to disseminate new revised QoS information of Web services, which not only maintains the scalability of the underlying Chord network, but also improves reliability and timelines guarantee especially for QoS information obtainment. The authors suggest specialized rendezvous points（RPs） and a replica mechanism to reduce the risk of subscriptions loss and consequently improve reliability. A reverse RP ring is designed to quicken subscription delivery and QoS information publication. In addition, an optimization mechanism for composite services is built into the proposed model, which helps to reduce notification traffic. Simulation results show that the model is featured by low cost, high efficiency and scalability, which is suitable to large-volume QoS information distribution.