【作者】 尹可挺；

【导师】 王申康； 周波；

【作者基本信息】 浙江大学 ， 计算机科学与技术， 2010， 博士

【摘要】 面向服务的计算(SOC)与面向服务的架构(SOA)是当前分布式计算和软件开发的最新发展方向,能够帮助企业更加快速、低价、灵活地构建应用程序和业务流程,而Web服务组合则是其中的关键技术。面对激烈的市场竞争,为了满足用户严格的要求,在服务组合的过程中需要根据QoS来选择Web服务,并在运行时持续监控与维护,以维持或改进组合服务的QoS指标,这个过程被称为基于QoS的服务组合。随着Internet及电子商务等技术的快速发展,越来越多的Web服务组合发生在Internet环境中。现有基于QoS的Web服务组合方法多是针对通用环境设计,没有考虑Internet环境中面临的一些新的问题与机会。本文围绕Internet环境中基于QoS的Web服务组合进行了研究,重点在于改进传统方法使之适应Internet环境、提出新的方法使之充分利用Internet环境的优势并进一步研究Internet环境带来的新问题,提出相应的解决方法。主要内容及贡献如下：1)研究将传统方法应用到Internet环境中基于QoS的Web服务组合时面临的基本问题,提出了基于整数线性规划的优化流程。分析了Internet多网络环境中Web服务组合面临的一些新问题,讨论了该环境中Web服务的QoS模型,研究了服务分布、引擎部署位置对组合服务性能的影响,从性能、安全等角度对传统基于QoS的服务选择方法进行了改进,并提出了基于整数线性规划的优化流程,仿真实验验证了方法的有效性,且其性能也是可以接受的。2)研究基于QoS的多粒度服务组合问题,提出了基于混合整数线性规划的多粒度服务选择方法。针对Internet环境中Web服务资源极为丰富的特点,提出并形式化定义了基于QoS的多粒度服务组合选择问题,通过引入“多粒度约束”条件,对此问题建立了混合整数线性规划模型并提出了完整的求解方案。该方法可扩展服务选择空间,得到更优的服务组合方案,仿真实验从性能、优化率和成功率三个方面验证了其有效性。3)研究QoS保证的Web服务组合维护问题,提出了保证QoS、基于自底向上的Web服务替换方法。为了适应Internet环境中动态变化的Web服务资源,保证组合Web服务持续满足业务要求,提出了一种能够保证QoS、基于自底向上的Web服务替换方法,用于替换组合中不能满足要求的成员服务。实验结果表明,该方法能够有效扩大替换服务的选择范围,替换结果优于传统方法,更好地确保组合服务的QoS指标得到维持和优化。4)研究Internet环境中成员服务之间存在的可靠性关联关系,提出了一种基于树的组合服务可靠性模型,并基于此改进了基于QoS的服务选择方法。将Internet环境中组合服务的共因失效因素分为四个层次,并提出了一种考虑了成员服务间关联关系的基于树的组合服务可靠性模型及相应的分析算法；同时,研究了基于QoS的Web服务选择中的共因失效因素,提出了组合后共因失效约束生成和组合前共因失效约束生成两种算法来避免或降低服务选择过程中共因失效因素的影响,确保组合服务的可靠性满足要求。5)设计并实现针对Internet环境中基于QoS的Web服务组合的实验系统。设计并实现了AQSCS(Advanced Quality-aware Services Composition System)实验系统,为本文提出的Internet环境中基于QoS的Web服务组合方法提供模拟环境与验证平台,该系统具有良好的扩展性,可作为进一步研究的基础实验环境。更多还原

【Abstract】 Service-Oriented Computing (SOC) and Service-Oriented Architecture (SOA) are new research directions in distributed computing and software development, which can help the enterprise to build applications and business processes more rapidly, cheaply and flexibly. Web service composition is the key underlying technology. In order to keep up with the fierce market competition and meet the users’ strict requirements, web services for the composition should be selected based on QoS and monitored continuously during runtime to keep or improve the QoS of web service composition. The process is called QoS-aware services composition.With the rapid development of Internet and e-commerce technologies, more and more web service compositions occur in Internet environment. Most of the current approaches for QoS-aware services composition are designed for generic environment, which don’t consider the specific requirements and challenges in Internet environment. In this thesis, we research on the problem of QoS-aware services composition in Internet environment and focus on the following three aspects:adapt traditional approaches to Internet environment, propose new approaches to make full use of the advantages in Internet environment, research on the new issues in Internet environment and provide corresponding solutions. Major work and contributions include:First, we research on the basic issues faced when applying traditional approach to the problem of QoS-aware services composition in Internet environment and propose a new optimizing process. We analyze new issues of web service composition in Internet environment, discuss QoS model of web service in the environment, investigate the influence of the services distribution and execution engine deployment location on the performance of composite web service, and propose an integer linear programming based optimization process which improves the traditional approach from the perspective of performance and security. Experiments show the effectiveness of the new approach and the performance is also acceptable.Second, we propose the QoS-based multi-granularity services composition problem and its solution. In order to fully utilize the abundant web services resources in the Internet, we propose and formally define the problem of QoS-based multi-granularity services composition (QMGSCP). By introducing the "Multi-Granularity Constraints", QMGSCP is formulated as a mixed integer linear programming problem. In this way, better composition solution can be achieved since more web services will be available as candidate. Experiments show the improvement in performance, optimization rate and success rate.Third, we research on QoS-guaranteed web service composition management problem and propose a QoS-based, bottom-up services replacement approach for web service composition. In order to adapt to the dynamically changing Web service resources in open environment and ensure that the composite web service meet the business requirements continuously, we propose a QoS-based, bottom-up services replacement approach. Experiments show that the proposed approach could find more candidate Web services for replacement thus maintain or improve the QoS of the composite Web service more effectively.Fourth, we research on the reliability correlation of component web services in Internet environment, propose a tree-based reliability model and improve the services selection process. We categorize common-cause failures (CCFs) of composite web service in Internet environment and propose a tree-based reliability model that considers the correlation of component services. Based on the model, we research on the CCF-aware QoS-based web service selection process and propose two algorithms (POST-CCG and PRE-CCG) to avoid or mitigate the impact of CCFs, thus to ensure that reliability of the web service composition meet the requirement.Last, we design and implement the experimental system AQSCS (Advanced Quality-aware Services Composition System). AQSCS provides simulation environment and implements the algorithms for QoS-aware services composition in Internet environment proposed in the thesis. The system is extensible and can be used as a basic platform for further research.更多还原