Analyzing conversations of Web services

A composite Web service consists of a set of individual services (or peers), which interact with each other via messages. A conversation is a global sequence of messages exchanged among peers participating in a composite Web service. Interestingly, conversation behavior differs significantly for synchronous and asynchronous communication, even if peers' local behaviors remain the same. The authors use synchronizability and realizability analysis techniques to analyze conversations in the presence of asynchronous communication. With these analyses, they can use model checking to automatically verify conversation behavior for bottom-up and top-down Web service specifications.     

Specification of realizable service conversations using collaboration diagrams

Specification, modeling and analysis of interactions among peers that communicate via messages are becoming increasingly important due to the emergence of service oriented computing. Collaboration diagrams provide a convenient visual model for specifying such interactions. An interaction among a set of peers can be characterized as a conversation. A conversation is the global sequence of messages exchanged among the peers, listed in the order they are sent. A collaboration diagram can be used to specify the set of allowable conversations among the peers participating to a composite web service. Specification of interactions from a global perspective leads to the realizability problem: Is it possible to construct a set of peers that generate exactly the specified set of conversations? In this paper, we investigate the realizability of conversations specified by collaboration diagrams. We formalize the realizability problem by modeling peers as concurrently executing finite state machines, and we give sufficient realizability conditions for a class of collaboration diagrams.     

Specifying and Validating Data-Aware Temporal Web Service Properties

Most works that extend workflow validation beyond syntactical checking consider constraints on the sequence of messages exchanged between services. These constraints are expressed only in terms of message names and abstract away their actual data content. We provide examples of real-world "data-aware" Web service constraints where the sequence of messages and their content are interdependent. To this end, we present CTL-FO⁺, an extension over computation tree logic that includes first-order quantification on message content in addition to temporal operators. We show how CTL-FO⁺ is adequate for expressing data-aware constraints, give a sound and complete model checking algorithm for CTL-FO⁺, and establish its complexity to be PSPACE-complete. A "naive" translation of CTL-FO⁺ into CTL leads to a serious exponential blowup of the problem that prevents existing validation tools to be used. We provide an alternate translation of CTL-FO⁺ into CTL, where the construction of the workflow model depends on the property to validate. We show experimentally how this translation is significantly more efficient for complex formulas and makes model checking of data-aware temporal properties on real-world Web service workflows tractable using off-the-shelf tools.     

Bounded phase analysis of message-passing programs

We describe a novel technique for bounded analysis of asynchronous message-passing programs with ordered message queues. Our bounding parameter does not limit the number of pending messages, nor the number of “context-switches” between processes. Instead, we limit the number of process communication cycles, in which an unbounded number of messages are sent to an unbounded number of processes across an unbounded number of contexts. We show that remarkably, despite the potential for such vast exploration, our bounding scheme gives rise to a simple and efficient program analysis by reduction to sequential programs. As our reduction avoids explicitly representing message queues, our analysis scales irrespectively of queue content and variation.     

基于WSE和消息队列的异步Web服务研究及实现

针对目前利用RPC方式难以真正实现异步Web服务的问题,提出了一种新的异步Web服务解决方案,即在WSE体系架构下,通过将SOAP协议与消息队列的绑定,完成SOAP消息的异步传递,从而实现Web服务的异步调用。     

基于Petri网的Web服务自动组合研究

根据Web服务中消息和行为的关系,Web服务被描述为面向消息的基于行为Petri网模型(Moap)．该模型包括消息域和服务过程,前者是服务协同以及和用户通信的通道,后者是基于Petri网的Web服务行为过程描述．Moap支持组合服务的重用,可以很好地描述可用服务的并行调用,另外元消息机制也有利于服务的自动组合．在Moap基础上,定义了服务组合系统和服务的协同;给出了服务自动组合规则,并证明了其有效性和完备性．最后,通过一个实例直观描述了服务组合系统的工作方式．     

MOM vs. RPC: communication models for distributed applications

An important aspect of designing a distributed application is the communication model we use to connect its various components. Some middleware solutions, such as Web services, offer two of the most important communication paradigms: asynchronous messaging and remote procedure call (RPC). Message-oriented middleware (MOM) lets a service's consumers physically and temporally decouple from the service providers. Communication between service providers and the consumers is asynchronous, and it don't need to be available at the same time because they communicate by sending and receiving messages from designated message queues. In contrast, RPC is a synchronous method of requesting remote service execution. Consumers must suspend service execution until they receive a reply from the provider. MOM and RPC have advantages and disadvantages. MOM solutions tend to be more robust to failures than RPC, and it allows service requesters to continue to process while service provider's work on their requests. However, programming MOM-based applications is more cumbersome because distribution isn't as transparent to the programmer as with RPCs. In this column, we provide a quantitative framework, which we can use to compare MOM- and RPC-based solutions.     

一种基于抽象与精化技术的Web服务组合验证方法

模型检测因其自动化程度高、能够提供反例路径等优势,被广泛应用于Web服务组合的兼容性验证。本文针对模型检测过程中存在的状态爆炸问题,在传统的模型检测方法中引入谓词抽象和精化技术,提出了一种针对Web服务组合的抽象精化验证框架。使用谓词抽象技术对原子Web服务抽象建模,将各Web服务抽象模型组合成组合抽象模型;将模型检测后得到的反例在各原子Web服务上做投影操作,对投影反例进行确认;对产生伪反例的Web服务抽象模型进行精化,生成新的组合抽象模型,再次对性质进行验证。最后通过实例分析说明基于抽象精化技术的Web服务组合验证框架在缓解状态爆炸问题上的可行性。     

基于Web服务的会话模型及其比较和应用研究

Web服务的基础规范仅支持具有简单交互协议的服务调用，不能支持需要交换一系列消息交换的复杂的电子商务交互。文中首先提出了基于Web服务的会话和会话模型的概念，试图用它们来解决双方或多方之间复杂的多步骤的长运行期的交互问题，然后从新兴的描述Web服务的会话性的各种标准归纳出两种会话模型，并对它们进行了详细的分析、应用和比较，最后给出基于会话的企业问应用集成模型，综合应用了基于这两种会话模型的标准。     

Web服务异步调用的研究与实现

虽然大部分的Web服务系统都支持异步调用,但是目前流行的One-Way式异步调用技术并不完善,在实现异步调用机制的同时增加了系统的运行压力。文中提出了基于回调机制和消息回执的Web服务异步调用模式,在不增加系统运行压力的情况下,实现了Web服务的异步调用,并能保证消息的可靠性。     

Web服务组合的基于文法的消息处理

Web服务作为一种新型的信息集成架构,已经受到了来自数据库领域和软件工程领域的广泛关注．在Web服务应用中,将多个服务组合成一个能完成复杂商业任务的组合服务技术是企业应用集成(EAI)的关键．在服务组合过程中,两个需要通信的服务之间的消息数据模式经常是不一致的,需要用户程序进行消息内容的获取和重组．这个问题在以往的研究中很少受到关注．该文首次形式化描述了服务间的接口信息处理问题．并且把服务组合中的接口信息处理问题转换为XML数据的处理问题,然后,引入基于文法的处理方法来解决接口数据之间的处理问题．实验表明了基于文法的接口数据处理技术提供了一种方便灵活的消息处理手段,可以解决复杂的信息处理需求,并且有较好的性能．     

Analysing a stream authentication protocol using model checking

In this paper, we consider how one can analyse a stream authentication protocol using model checking techniques. In particular, we will be focusing on the Timed Efficient Stream Loss-tolerant Authentication Protocol, TESLA. This protocol differs from the standard class of authentication protocols previously analysed using model checking techniques in the following interesting way: an unbounded stream of messages is broadcast by a sender, making use of an unbounded stream of keys; the authentication of the n-th message in the stream is achieved on receipt of the n+1-th message. We show that, despite the infinite nature of the protocol, it is possible to build a finite model that correctly captures its behaviour.     

Simulating perfect channels with probabilistic lossy channels

We consider the problem of deciding whether an infinite-state system (expressed as a Markov chain) satisfies a correctness property with probability 1. This problem is, of course, undecidable for general infinite-state systems. We focus our attention on the model of probabilistic lossy channel systems consisting of finite-state processes that communicate over unbounded lossy FIFO channels. Abdulla and Jonsson have shown that safety properties are decidable while progress properties are undecidable for non-probabilistic lossy channel systems. Under assumptions of “sufficiently high” probability of loss, Baier and Engelen have shown how to check whether a property holds of probabilistic lossy channel system with probability 1. In this paper, we consider a model of probabilistic lossy channel systems, where messages can be lost only during send transitions. In contrast to the model of Baier and Engelen, once a message is successfully sent to channel, it can only be removed through a transition which receives the message. We show that checking whether safety properties hold with probability 1 is undecidable for this model. Our proof depends upon simulating a perfect channel, with a high degree of confidence, using lossy channels.     

一种基于扩展有限自动机验证组合Web服务的方法

为简化并自动化组合Web服务验证,提出一种基于扩展有限自动机(extended deterministic finite automata,简称EDFA)验证组合Web服务的方法.使用EDFA可以准确地描述Web服务:EDFA的状态表达Web服务在与用户交互的过程中维护的状态;EDFA的状态转移及其标注描述Web服务与用户间的消息交换.EDFA给出Web服务交互过程的所有消息交换序列,刻画出Web服务的动态行为.使用基于EDFA的组合Web服务验证方法不但可以验证组合Web服务是否满足系统需求,还可以验证组合Web服务运行过程是否有逻辑错误.与其他方法相比,该方法更适于验证开放式环境下的组合Web服务.     

基于PDG图的分布式动态可执行服务组合方法

组合服务是将一系列Web服务协调地组合在一起,从而完成预期目标。组合服务按照其引擎分布可分为:集中式服务组合和分布式服务组合。分布式组合服务可以有效地解决集中式组合服务在系统可伸缩性、消息传输效率、自治性和有效负载均衡等方面的问题,将可执行全局流程等价分解成可执行本地流程,以及将服务组合和负载均衡结合集群概念,研究服务组合的QOS。这些将成为新的挑战,文中通过PDG图进行等价分解,并结合QOS,通过实验测试引擎负载,提出将负载均衡融入服务组合QOS研究思想。     

基于时间自动机的Web服务模型检测

传统的基于有限状态机的组合Web服务模型检测方法不能保证带有时间约束的组合Web服务的正确性.把组合Web服务看成多智能体系统,将带有时间约束的Web服务智能体建模为时间自动机,通过并发组合构成时间自动机网络,从而用时间自动机验证工具UPPAAL对组合Web服务的运行过程进行模拟,并验证其活性、安全性和死锁等性质.采用该方法对雇员出差安排组合Web服务进行建模和验证,结果表明,该组合Web服务存在死锁问题.最后通过分析死锁产生的路径,完善该组合Web服务的通信协议,从而消除了死锁.     

一种高效的Web服务性能优化策略

Web服务是构建面向服务架构(SOA)的主流分布式计算技术.基于XML的数据传输格式在给Web服务带来众多优点的同时,严重影响了其性能,制约了Web服务的应用.众多研究表明,XML解析和数据绑定是Web服务的主要性能瓶颈.着眼于避免传统XML解析和运行时Java反射过程的开销,提出了一种新颖的Web服务性能优化策略.它为每个Web服务生成一个特定于该服务的SOAP消息处理器,通过在对SOAP消息的一遍扫描中高效地生成服务业务逻辑调用所需的参数对象.实验结果表明,该优化策略能够有效地提高Web服务的性能.     

基于软件代理和上下文的Web服务合成方法

Web服务的诸多特性使得它非常适合于商务应用集成，工业界和学术界都希望能够通过合成多个Web服务从而获得增值的新服务。介绍两个概念以减少Web服务合成的复杂性：软件代理和上下文；并论述了在合成期间，软件代理之间进行会话以同意Web服务参与到合成中。     

Dragonmail: An exercise in distributed computing

A conversation-based message system groups related messages into conversations and orders messages within conversations according to the context in which they were submitted. This paper describes the implementation of a comprehensive conversation-based message system, called Dragonmail, that extends an earlier prototype in two ways. First, it integrates conversations with conventional memo-based mail in a way that preserves the semantics of the conversation abstraction. Secondly, it provides for the distribution of software components across multiple hosts to support remote interfaces.     

基于uMSD的Web服务组合验证方法研究

手工分析组合服务相当困难和耗时,为此提出了一种基于uMSD的Web服务组合的模型检验方法.如何简单和直观地表示Web服务组合的时态性质是该方法的关键问题.鉴于uMSD在简单性和表达力之间找到了一个平衡点,定义了uMSD的形式语法和语义.以Web服务组合OJA为实例,使用uMSD来图形化地表示组合服务的时态性质,展示了u...