On Distributed QoS Management And Key Techniques For Web Services

Web service QoS or quality of web service is the non-functional attributes of a service, e.g. reliability, response time. QoS is critical to user experience of services. In an open service market, a large number of services may spread in different areas and belong to different business organizations. How to manage QoS in such an environment and provide an open, reliable environment for users to employ services becomes a crucial problem in web service research.In literature, QoS management approaches are based on centralized QoS brokers, which have potential performance and scalability problem, and more importantly, the centralized approaches can not support cross-domain QoS management for web services. In recent years, a major trend in web service research is on distributed infrastructure by leveraging the thoughts of P2P computing, but distributed QoS management has not been substantially explored yet. Based on current status of QoS management and web service research, we address several critical problems in distributed QoS management. The contribution of this dissertation includes:1. Propose an independent distributed QoS registration approach. QoS information is dynamic and everchanging, so currently known distributed service registry works are not suitable to QoS management problem. We propose an independent distributed QoS registration approach where the QoS storage and service functional data storage is separated (The system is called Q-Peer). By analyzing the QoS accessing behavior of users, we propose a highly efficient QoS query approach which achieves query efficiency close to centralized registry.2. Propose a load-balance approach for distributed QoS registry. To utilize the resource of distributed registry, and achieve load-balance, we research the difference on load information between Q-Peer and other P2P network. We propose two effective data replication schemes. Based on the schemes we propose a novel replication scheme by peer negotiation to improve the efficiency in replication. Experimental results show that the replication scheme improves registry utility significantly.3. Propose an iterative selection algorithm for composite service. Known selection approaches requires the information of complete composite service topology and all the QoS of candidate services, which is not applicable in Q-Peer, so we propose an iterative selection algorithm, which can optimize composite service across multiple peers. The experimental results proved that the algorithm achieves excellent selection result and outperforms current selection approaches. The iterative selection algorithm can be applied to dynamic selection naturally. The algorithm includes network QoS as optional factors, which makes the algorithm applicable for network sensitive service.4. Propose an event-driven distributed QoS monitoring approach. To address the problem of known QoS monitors which are not capable of monitoring cross-domain services and not flexible in monitoring complex and personalized QoS, we propose an event-driven distributed QoS monitoring approach. The approach bases on ECA rules and event stream model, to provide run-time QoS exception handling and long-term metric collection. We further propose an event routing mechanism for flexible monitoring cross-domain composite service in distributed QoS management environment. At last, we propose a policy-based requirements description approach to support user configuration for personalized QoS monitoring.5. Propose a distributed QoS management system. Based on our research on the problems in distributed QoS management, we extend Q-Peer registry to a distributed QoS management system as the supporting platform for management capabilities. Q-Peer is an overlay network for QoS management, which is formed by a large number of independent peers. Peers coordinate with each other by standard web service protocols and keep autonomy by role-based access control policy. On Q-Peer, the QoS management capabilities are deployed as applications over access control and communication infrastrusture. The Q-Peer achieves extensibility of management functions as well as management domains.