支持web服务合成系统可靠性的工作流恢复机制的研究.doc

支持Web服务合成系统可靠性的工作流恢复机制的研究
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摘 要
当前，Web服务作为新的分布式计算技术，由于其自身的平台无关、服务器中立、自描述以及易部署等特性，已经被越来越广泛地接受。许多企业已将自身的业务能力以Web服务的形式提供给消费者。在众多的Web服务出现时，一个新的商机出现了——合成的Web服务，即将现有的Web服务重新整合起来，以形成一个功能更强大的Web服务。Web服务合成是一个企业通过合成基本的Web服务,来提供给用户增值服务的能力。
对于合成后的平台，如何保证系统运行的可靠性是一个必须要解决的问题。Internet环境的开放式、分布式的特点使得构建于其上的系统更加难以控制；网络传输的可靠性本身就受到其底层硬件平台稳定性的制约；Web服务自身异构性、自治性和无状态性的特点也大大增加了保证合成平台可靠性的难度。而且，Web服务合成的实现方法也是影响其可靠性的重要因素。
目前，基于工作流技术的合成已成为Web服务合成的重要方法。工作流是描述一个企业或组织的业务处理过程的模型，一直是企业界和学术界的热点研究领域。在本系统设计和实现之前，我们在工作流领域已经取得了一定的研究成果——完全分布式的面向大规模复杂应用的工作流管理系统ScopeWork。该系统对包括恢复处理在内的多项工作流技术均提出了较为完备的解决方案。
现在，Web服务的合成正是应用了工作流的技术，在完全自治的Web服务上搭建合成平台。因此，基于Web服务合成系统可靠性的保证完全可以借鉴工作流恢复的思想。本文提出的系统正是基于ScopeWork系统的研究基础，利用已掌握的、较为成熟的工作流技术来实现Web服务的合成。为了保证合成系统的运行可靠性，我们设计并实现了一个恢复系统，该系统包括检测模块、监控模块和恢复模块，分别完成故障检测、流程监控及恢复处理等功能。为了更好地满足合成系统可靠性的要求，我们从多个方面对工作流的恢复理论进行了扩展：对系统中可能出现的运行异常重新进行分类；对传统工作流中的任务结构模型进行了扩展；根据本系统的特点提出了面向系统不同层次的三层异常检测模型；针对合成系统中不同类型的流程，我们分别采用不同的恢复策略来处理异常情况。通过这些工作，我们大大提高了系统的错误处理能力。

关键词 Web服务合成 工作流 恢复 故障检测 错误处理
Research of Workflow Recovery Mechanism Supporting Reliability of Web Service Composition System
Abstract
Web service, as a new distributed computing technology, has been accepted currently because of its features such as platform independence, server neutrality and self-description. Now many enterprises provide consumers with business ability in manner of Web service. With more and more Web services’ coming forth, a new commerce opportunity, composition of Web services, appears. We can distribute a more powerful Web service, which is composed of existing Web services, to provide added value.
When compositing, we must take into account system reliability. Open and distributed Internet environment makes systems based on it difficult to control; Reliability of network transmission is restricted because of its underlying hardware; The feature of heterogeneity, autonomy and status independence also greatly increases difficulty. Furthermore, the way of composition is also an important factor that will infect system reliability.
Workflow technology has become the most important way of compositing Web services. Workflow, as a hotspot in both academe and business field, is a model that describes handling process inside an enterprise or organization. Before our work on composition system, we have got deeply research in the field of workflow and developed a wholly distributed WFMS ScopeWork, which have put forward a full resolution, including error handling.
Since we use workflow technology to composite Web services, when we try to ensure the reliability of composition system, we can use theory of workflow recovery for reference. The system this thesis advanced is just based on the research of WFMS ScopeWork. To ensure its reliability, we design and implement a recovery system, including detecting module, monitoring module and recovery module, which accomplish the function of failure detecting, process monitoring and recovery handling respectively. To satisfy the reliability requirement, we extend theory of workflow recovery in many aspects, including renewedly classifying runtime exceptions, extending task structure, advancing a three-level failure detecting module oriented different levels of the composition system, using different recovery strategies to handle different types of flows. In summary, we enhance ability of error handling greatly in composition system of Web services.

Key words Web service composition, workflow, recovery, failure detection, error handling目录
声 明 I
摘 要 II
ABSTRACT IV
目录 VI
第一章 引言 1
1.1 问题的提出 1
1.2 当前的研究现状 4
1.3 本文的组织结构 5
第二章 关键技术 7
2.1 Web服务 7
2.1.1 Web服务的定义 7
2.1.2 Web服务的体系结构 8
2.1.3 Web服务的特点 9
2.1.4 Web服务的标准 11
2.2 Web服务合成 13
2.2.1什么是Web服务合成 13
2.2.2 Web服务合成的主要问题 13
2.2.3 Web服务合成的方法 15
2.3 工作流技术 15
2.3.1 工作流的提出 15
2.3.2 工作流管理系统 16
2.3.3 工作流的基本概念 17
2.3.4 工作流管理系统的体系结构 18
2.4 工作流恢复技术 20
2.4.1 工作流恢复的研究现状 20
2.4.2 先进事务模型（ATM） 21
2.4.3 工作流中的异常及其分类 24
2.4.4 工作流的恢复策略 24
2.4.5 工作流的恢复手段 25
第三章 恢复系统的总体结构 27
3.1 开发环境 27
3.2 恢复系统结构框架 29
第四章 日志记录及流程监控 33
4.1 任务结构的扩展 33
4.2 日志仓储结构 35
4.3 日志的记录 35
4.4 流程监控器的设计 37
第五章 故障检测机制 39
5.1 “错误”建模 39
5.2 三层检测模型 41
第六章 恢复策略 44
6.1 Web服务合成流程的种类 44
6.2两种恢复策略 45
总结与展望 48
参考文献 49
攻研期间论文发表情况 51
攻研期间科研情况 52
致 谢 53

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