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题名:
事务性Web服务复合关键技术研究
作者: 丁晓宁
答辩日期: 2007-06-06
授予单位: 中国科学院软件研究所
授予地点: 软件研究所
学位: 博士
关键词: Web服务 ; 事务处理 ; 服务复合 ; 并发控制 ; 失败恢复 ; WS-BPEL
其他题名: Research on Transactional Web Service Composition
摘要: Web服务 (Web Services)是构造下一代分布式计算平台的基本技术。单个Web服务所能够提供的功能有限,服务复合(Service Composition)通过组合现有的Web服务从而创建新的、高层的Web服务以完成更复杂的任务,是构建Web服务平台应用的重要手段。 事务处理(Transaction Processing)是保证分布式系统可靠性的关键技术,保证了服务复合获得正确的、一致的执行结果。目前对Web服务事务的研究尚处于初始阶段,主要研究成果形成了WS-Transaction、BTP、WS-TXM等事务规范,这些规范定义了事务参与者之间的消息交换协议,解决了最基本的互操作性问题。然而,对于如何基于事务机制来构造可靠的Web服务复合仍然缺乏研究。在理论上,当Web服务事务放松了原子性和隔离性后,如何为事务性服务复合提供灵活的松弛原子性,如何有效地进行并发控制和失败恢复等都缺乏系统的研究;在应用上,现有的服务复合描述语言如WS-BPEL等只定义了服务复合的功能性需求,对事务特性支持不足,与已有的事务规范族是独立的两套规范族。 针对上述问题,论文按照Web服务复合的生命周期顺序,根据事务性复合服务(Transactional Composite Service, TCS) 与传统事务的差异,对TCS若干关键技术给出了我们的解决方案,包括在设计期的静态结构描述与检查,运行期的分布式并发控制以及失败恢复等。 首先,给出了一个事务性服务复合模型TSCM (Transactional Service Composition Model),一个具体的事务性复合Web服务就是TSCM模型的一个实例。TSCM刻画了Web服务的不同事务属性,计算了各个事务属性从最底层的原子服务向上的传播。TSCM模型的特色在于支持用户自定义的松弛原子性,从而可以灵活刻画各种特定应用需求与用户偏好,并给出了相应的松弛原子性标准、判定定理与算法。 其次,当前的Web服务松弛事务模型放松了TCS之间的隔离性,当多个TCS并发执行时可能产生非串行化与非持久化的调度,需要对其进行并发控制。相比传统的事务并发控制,TCS并发控制的特征在于它跨Internet的完全分布性和自治性。我们提出了一个分布式并发控制协议TSCM-CC,并证明了该协议所产生的调度是冲突可串行化和持久的。TSCM-CC通过明确操作的持久化状态,丰富了依赖关系类型,保证了服务原有的事务属性。 然后,针对TCS执行中可能出现的故障,提出了一个松弛原子性驱动的失败恢复算法TCSM-FR。由于利用了自定义松弛原子性中蕴涵的应用语义,TSCM-FR更加准确高效,避免了不必要的失败恢复,而且在覆盖范围上涵盖了事务管理功能,有效地分离了关注点。同时,TSCM-FR充分考虑了TCS的特点,支持多绑定服务、预定义异常处理句柄等方式,尽可能地提高继续执行的可能性,降低失败恢复的代价。 最后,我们选择当前应用最广泛的Web服务复合描述语言WS-BPEL,将本文的研究应用到其中,为其扩充事务属性。扩充后的新语言我们称之为WS-BPEL/T (WS-BPEL/Transaction),它与标准的WS-BPEL语言是兼容的。我们的扩充包括语法元素扩充、部署描述符规范扩充、与原有异常处理机制的整合、与原有补偿机制的整合等,并应用在中科院软件所自行开发的Web服务复合引擎OnceBPEL中。
英文摘要: Web Service is the most promising technology to build next generation distributed computing. A single service can only perform limited functions, and service composition is the primary approach to build web service based applications, which creates a new value-add service from existing individual services. Transaction processing is the key technology to keep distributed computing reliable. To build a reliable web service composition, it is necessary to do a transactional service composition. Current research on web service transaction is still in its infant. The research result was mainly presented as three specifications: WS-Transaction, BTP and WS-TXM. These specifications define message exchange protocols among transactional participants and some interoperation issues, but did not state how to integrate transactions into service composition. It is still a difficult problem to build a reliable transactional web service composition. For example, how to define and check flexible relaxed atomicity constraint, how to maintain consistency under relaxed isolation, how to perform an efficient failure recovery, etc. Additionally, current service composition language such as WS-BPEL lacks the support of transactions, and is separated from web service transaction specifications. To solve above problems, this paper investigates the difference between transaction composite service (TCS) and the traditional transaction processing, and discussed several key technologies in transactional service composition according to the lifecycle of TCS, including relaxed atomicity specification and checking, distributed concurrency control, failure recovery, etc. First, we propose a transactional service composition model TSCM, where a concrete transactional composite service is an instance of the model. TSCM category different types of transactional services, describe their transactional properties, and calculate the propagation of the transactional properties from primitive service to composite service. The feature of our model is the supporting of customized relaxed atomicity constraint, which can express some application-specific requirements and user preference. We also give the according relaxed atomicity criterion and checking theorem. Secondly, current relaxed transaction models relax isolation among multiple web service transactions, which may produce a non-serializable and non-durable scheduling. It is need to perform a concurrency control among multiple TCS. The feature of TCS concurrency control is its pure distributing and autonomous. We propose a distributed concurrency control protocol TSCM-CC, and proved that the scheduling generated by TSCM-CC is serializable and durable. TSCM-CC employs lots of policies to preserve the original transactional type of services, such as durable state of operations, enhance dependency types, dynamic detecting of cycle dependency, etc. Then, we propose a relaxed atomicity-driven failure recovery algorithm TSCM-FR to handle the possible failures during the execution of TCS. Utilizing the implicit application semantics in customized relaxed atomicity, the failure recovery works are performed more precisely. Furthermore, transaction management works are integrated into our algorithm. The routine transactional works, such as retrying service or compensating service are performed by system automatically instead of users manually. Thus the non-functional concern is separated from business logic. Using the feature of TCS, TSCM-FR supports service multi-binding and user-defined exception handling mechanism, which improves the probability of further execution. Finally, we apply our theory into the most widely used language WS-BPEL and enhance it with full transactional feature. The extended language is named WS-BPEL/T. Our extension includes four parts: new syntax elements, new deployment descriptors, integration with original exception handling mechanism and integration with original compensation mechanism. The new language is implemented in OnceBPEL, a WS-BPEL engine which developed on our own.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.iscas.ac.cn/handle/311060/5782
Appears in Collections:中科院软件所

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Recommended Citation:
丁晓宁. 事务性Web服务复合关键技术研究[D]. 软件研究所. 中国科学院软件研究所. 2007-06-06.
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