【作者】 何丰；

【导师】 乐嘉锦；

【作者基本信息】 东华大学 ， 控制理论与控制工程， 2008， 博士

【摘要】 Web服务组合作为一种崭新的分布式计算模型,是Web上服务集成的有效机制。随着Web服务成为公认的实现服务的主流技术选择,这使得动态Web服务组合技术成为面向服务的计算的核心技术。目前,许多国内外研究机构围绕动态Web服务组合技术展开研究工作,并取得了一些有价值的探索性成果。然而,Web服务组合还有许多需要进一步研究的问题。根据Web服务组合的生命周期,展开动态Web服务组合关键技术研究,重点在:Web服务和Web服务组合的形式化模型,Web服务自动组合的推理算法,Web服务组合的正确性验证,Web服务组合的异常处理。主要工作与贡献包括如下五个方面:1.利用标签颜色Petri网(LCPN)方法对OWL-S描述的语义Web服务原子与复合进程的过程模型进行形式化建模。为建立动态的Web服务组合模型提供了有效的逻辑基础。然后,定义了一种基于层次颜色Petri网(HCPN)的Web服务组合模型WSC HCPN。通过自顶向下的服务分解的方法支持层次化Web服务组合描述,并以图形方式表示Web服务间的逻辑依赖,清晰、直观的刻画了Web服务组合。2.借助基于接口匹配的服务组合思想,将Web服务抽象成由输入和输出组成的实体,分析了各种服务依赖关系,建立了服务发布图;然后,借鉴了人工智能的思想,采用基于模糊推理Petri网的推理方法,通过反向、正向推理算法从服务发布图中提取出Web服务组合模型,实现了自动组合。由于采用了基于矩阵运算的正向、反向推理算法,并且支持并行处理,提高了组合效率,适合于大规模、复杂情况下的Web服务自动组合。3.提出一个基于Petri网的形式化验证技术对Web服务组合过程进行分析及验证,以保证服务组合的正确性和可靠性。此方法包含结构验证、可靠性验证两个部分。首先,利用转移矩阵(Transitive Matrix)分析方法对组合模型进行了可达性分析并检测是否有死锁。这种方法能有效地检验组合模型的结构正确性。然后,描述了基本Web服务的可靠性属性,将其引入到Web服务组合的模糊推理Petri网模型FRPN中以模拟和验证Web服务组合整体的可靠性。算例结果证实了该方法的有效性。4.在对Web服务的事务类型、事务状态以及事务依赖进行形式化描述的基础上,提出了一种ECA规则驱动的方法以处理服务组合中的可预测异常,建立了相应的Petri网模型。模型的优点是具有可扩展性以及适应性。然后对于不可预测异常,本文提出了一个层次式的异常恢复算法以保证服务组合的语义原子性。该算法依据层次间的事务依赖和服务的各种不同恢复特性进行层次式的向上规约处理,动态确定补偿终止点。此算法主要目的是有效减小补偿域。5.开发了一个基于颜色Petri网的Web服务组合原型系统CPN4WSC。上述方法和算法的适用性和有效性在原型系统CPN4WSC中得到了验证。综上所述,本文对Web服务自动组合问题中的几个关键问题进行了有效的探索与尝试,使用Petri网形式化技术提出了具体的解决方法,对于推进动态服务组合技术的理论研究和实用化具有一定的理论价值与应用价值。更多还原

【Abstract】 As a new application model for decentralized computing, Web services composition is becoming an effective mechanism for the services integration on the Web. Along with the acceptance of Web Services as the mainstream technology for service provision, dynamic service composition based on Web Services has been regarded as one of the core technologies for the service-oriented computing paradigm. Many research institutions home and abroad have conducted quite a few researches on dynamic service composition, and have made some valuable achievements.However, Web service composition still has many problems need further study. We start our research according to the life-cycle of a Web service composition, and focus on the following key technologies in this paper: Formal model for Web services and Web services composition, Automatic Web services composition reason algorithm, Correctness verification of Web services composition, Exception handling approach for Web services composition. The major work and contributions of this dissertation are as follows:1. Putting forward a formal approach to model OWL-S based semantic web services atomic and composite processes operational semantic with Label Color Petri Nets (LCPN). It provides a more effective logical foundation to build dynamic web services composition model. Then, A Hierarchical Color Petri Nets (HCPN) Model named as "WSC_HCPN" for Web service composition is proposed. The model supports hierarchical describe of web service composition and presents the logical dependency of services graphically though Top-clown service decomposition method. Therefore the model can describe web service composition clearly and intuitively.2. According to the Web Services dependency rules, a reasoning Petri nets (RPN) model to represent the production rules of the available services in a local repository. Based on the RPN model, a formal reasoning algorithm was proposed to perform web services composition reasoning automatically. With the method of matrix operation used in the algorithm, the reasoning process of web services composition is accomplished more simply, quickly, and its efficiency is also improved due to the parallel operation ability of Petri net. Specially, it fits reasoning for the large-scale web services composition problem.3. Putting forward a Petri-Net-based formal verification technique to analyze and verify the services composition process in order to ensure the correctness and reliability of the composition. The approach consists of two parts involve structure verification and reliability verification. At first, It utilize Transitive Matrix analysis methods to analyze reachability of the composition model and check whether there are deadlocks. This method validates the structure correctness of composition model. Then, Describing the reliability attributes of basic web service, and the reliability parameters are introduced into Fuzzy Reasoning Petri Nets model of web service composition (FRPN) for simulating and verificating the whole reliability of Composite Web Services. The effectiveness of this method is proved by the results of the samples.4. Based on describing transaction type, transaction state and transaction dependency of web services by means of an intuitional formal presentation formal presentation. First, A ECA rule-driven expectable exception handling method for Web service composition was proposed and corresponding Petri net model was established. The advantage of this model is extensibility and adaptability. Then we propose a hierarchical exception recovery algorithm for unexpectable exception to ensure semantic atomicity of services composition. The algorithm determines the end compensation point dynamically in a hierarchical bottom-up manner according to transaction dependencies across hierarchies and diverse recovery behaviors of different services. The primary goal of it is to reduce the compensation sphere.5. A prototype named CPN4WSC is developed based on CPN Tools for web services composition. The usability and validity of the above methods and algorithms are proven by CPN4WSC.To sum up, this dissertation tries to do useful works on some key issues of dynamic service composition, with formal technologies of Petri nets and sets up concrete methods to solve these problems. We believe that our contributions make a nice groundwork for research and engineering on dynamic service composition both in theory and practice.更多还原