Timed verification of hierarchical communicating real-time state machines

Hierarchical Communicating Real-Time State Machines (H-CRSM) is a formal modelling language for the modular development of distributed real-time systems. The formalism is characterized by the use of state transitions with guarded commands and timing constraints, the adoption of a few distilled statecharts constructs, and the modular specification of timing constraints along a state hierarchy. This paper proposes a translation of H-CRSM into Uppaal which enables model checking. Translation rests on unfolding a hierarchical model on a flat representation. The resultant approach is demonstrated by means of a case study.     

Analysis of a class of communicating finite state machines

Thereachability, deadlok detection andunboundedness detection problems are considered for the class ofcyclic one-type message networks of communicating finite state machines. We show that all the three problems are effectively solvable by (a) constructing canonical execution event sequences which belong to a context-free language, and (b) showing that the reachability sets are semilinear. Our algorithms have polynomial complexity in terms of size of a global structure of a network, called theshuffle-product. The relationships between general Petri nets and the class of communicating finite state machines considered here are also explored.Supported in part by NSF CCR-9004121     

A toolset in Java2 for modelling, prototyping and implementing communicating real-time state machines

This paper proposes an approach to the development of real-time systems which depends on Communicating Real-Time State Machines (CRSMs) as the specification language, and on a customisable actor kernel for prototyping, analysis and implementation of a modelled system. CRSMs offer an intuitive and distributed specification of a system in terms of a collection of co-operating state machines interacting with one another through timed CSP-like I/O commands. On the other hand, the underlying actor framework provides a time-sensitive scheduling structure which can be tuned to CSRMs in order to support temporal validation through assertions on the recorded time-stamped event histories. The approach can be practically used through a graphical environment (jCRSM) which has been realised using Java2. The toolset facilitates editing, testing and implementation in Java of CRSM systems. The proposed methodology is novel in that it provides a seamless system development life cycle where the specification, analysis, design and implementation phases are unified by a common representation of machines in terms of actors. The paper demonstrates the use of CRSM based software components by means of examples.     

Reverse reachability analysis: A new technique for deadlock detection on communicating finite state machines

The communicating finite state machines can exchange messages over bounded FIFO channels. In this paper, a new technique, called reverse reachability analysis, is proposed to detect deadlocks on the communication between the communicating finite state machines. The technique is based on finding reverse reachable paths starting from possible deadlock states. If a reverse reachable path can reach the initial global state, then deadlock occurs. Otherwise the communication is deadlock-free. The effectiveness of the technique has been verified by some real protocols such as a specification of X.25 call establishment/clear protocol and Bartlet's alternating bit protocol.     

Web Services的安全性

通过对现有的Web Services服务中存在的包括数据保密性、完整性、用户身份的认证和交易的不可抵赖性的4个涉及安全性问题的分析和研究，提出了解决这4个方面问题的解决方案，最后指出了Web Services的发展前景。     

用BPMN辅助整合Web Services

介绍了用BPMN设计整合Web Service,并产生Web Service描述语言(WSDL)形式的可执行规范语言,以及利用WSDL可以转换成业务流程管理标识(BPMN)的方法,动态地将已存在的Web Service通过BPMN图形化建模方法进行整合.鉴于BPMN的图形化设计,可以选择喜欢的可执行语言来实现该整合方案,主要采用与BPMN密切关联的Web Service语言--面向服务的业务流程可执行语言(BPEL4WS).     

Affinity-aware modeling of CPU usage with communicating virtual machines

Use of virtualization in Infrastructure as a Service (IaaS) environments provides benefits to both users and providers: users can make use of resources following a pay-per-use model and negotiate performance guarantees, whereas providers can provide quick, scalable and hardware-fault tolerant service and also utilize resources efficiently and economically. With increased acceptance of virtualization-based systems, an important issue is that of virtual machine migration-enabled consolidation and dynamic resource provisioning. Effective resource provisioning can result in higher gains for users and providers alike. Most hosted applications (for example, web services) are multi-tiered and can benefit from their various tiers being hosted on different virtual machines. These mutually communicating virtual machines may get colocated on the same physical machine or placed on different machines, as part of consolidation and flexible provisioning strategies. In this work, we argue the need for network affinity-awareness in resource provisioning for virtual machines. First, we empirically quantify the change in CPU resource usage due to colocation or dispersion of communicating virtual machines for both Xen and KVM virtualization technologies. Next, we build models based on these empirical measurements to predict the change in CPU utilization when transitioning between colocated and dispersed placements. Due to the modeling process being independent of virtualization technology and specific applications, the resultant model is generic and application-agnostic. Via extensive experimentation, we evaluate the applicability of our models for synthetic and benchmark application workloads. We find that the models have high prediction accuracy — maximum prediction error within 2% absolute CPU usage.     

Unboundedness detection for a class of communicating finite-state machines

Let M and N be two communicating finite-state machines that exchange one type of message. We discuss an algorithm to decide whether the communication between M and N is bounded. The algorithm is based on constructing a finite representation of the reachability tree of M and N assuming that M and N progress at equal speeds.     

Web服务的控制集成

在软件集成的研究中,控制集成是一个重要的组成部分,研究了Web服务的控制集成,提出了Web服务的包容模型与聚合模型,包容模型使用容器对Web服务进行封装,对外提供统一的服务访问接口,Web服务消费者通过该接口访问Web服务;聚合模型使用聚合器对Web服务进行管理,聚合器本身不参与Web服务调用,它向Web服务消费者提供Web服务的链接,Web服务消费者在从聚合器处获得链接后再访问相应的服务,其成果已经在一个原型系统中得到了验证.     

Web Services中的消息通信研究

首先介绍了Web Services的体系结构与基本可交互协议栈,然后介绍了消息通信的基础,提出在Web Services中通过消息通信机制能很好地解决传统RPC技术存在的性能、可靠性和多点支持的问题,接着详细描述了Web Services中进行消息通信的两个关键组成部分：缓冲和回调;最后通过示例讲述了创建Web Services消息通信的过程。     

语义网服务中的本体综述

作为实现下一代Web的集成方案,语义网服务将语义Web技术和Web服务技术相结合,以支持Web服务的自动发现、选择、合成和执行.本体是语义网服务的理论基础.介绍了Web资源描述本体OWL和Web服务描述本体的概况,并对3种主流的Web服务语义描述框架进行对比分析,为语义网服务中本体的创建提供基础知识.研究了语义网服务中存在的各层次的本体异构问题,明确了语义网服务中本体集成的主要研究方向.     

Understanding user perceptions of World-wide web environments

Abstract The purpose of this study was to develop and test a conceptual model of individual perceptions of Web technology as a use and training tool. The model presents a perspective of users' attitudes toward Web environments. This model integrates the Technical Acceptance Model, Social Cognitive Theory, individual attitudes, motivation and self-efficacy perspectives to develop a new aspect of users' perceptions toward Web technology acceptance and use. The study provides some evidence that the conceptual model helps the understanding of user perceptions to Web environments. In addition, training and educational programmes on computers may foster a positive feeling towards the Web. Furthermore, the more individuals have self-efficacy towards Web technology, the more individuals have motivation to use the Web.     

Web服务安全体系结构研究

随着Web服务的普及,构建解决其各种安全问题的安全体系结构研究变得非常有意义。在分析了Web服务的基本组件、协议以及Web服务所需要的安全保证之后,提出了一种分层的安全体系结构。该体系结构充分利用了现有的安全技术和设施,综合了传输层次和SOAP层次上的安全措施来保证Web服务的安全。另外还对各层次上应采取的措施和应达到的安全性要求做了详细的分析。     

Consumer-centric QoS-aware selection of web services

There exist many web services which exhibit similar functional characteristics. It is imperative to provide service consumers with facilities for selecting required web services according to their non-functional characteristics or quality of service (QoS). However, the selection process is greatly complicated by the distinct views of service providers and consumers on the services QoS. For instance, they may have distinct views of the service reliability—wherein a consumer considers that a service is reliable if its success rate is higher than 99%, while a provider may consider its service as reliable if its success rate is higher than 90%. The aim of this paper is to resolve such conflicts and to ensure consensus on the QoS characteristics in the selection of web services. It proposes a QoS Consensus Moderation Approach (QCMA) in order to perform QoS consensus and to alleviate the differences on QoS characteristics in the selection of web services. The proposed approach is implemented as a prototype tool and is tested on a case study of a hotel booking web service. Experimental results show that the proposed approach greatly improves the service selection process in a dynamic and uncertain environment of web services.     

Location-based services in ubiquitous computing environments

This paper presents a framework for providing dynamically deployable services in ubiquitous computing settings. The goal of the framework is to provide people, places, and objects with computational functionalities to support and annotate them. Using RFID-based tracking systems, the framework detects the locations of physical entities, such as people or things, and deploys services bound to the entities at proper computing devices near where they are located. It enables location-based and personalized information services to be implemented as mobile agents and operated at stationary or mobile computing devices, which are at appropriate locations, even if the services do not have any location-information. This paper presents the rationale, design, implementation, and applications of our prototype infrastructure.     

Computing refactorings of state machines

For behavior models expressed in statechart-like formalisms, we show how to compute semantically equivalent yet structurally different models. These refactorings are defined by user-provided logical predicates that partition the system’s state space and that characterize coherent parts – modes or control states–of the behavior. We embed the refactorings into an incremental development process that uses a combination of both tables and graphically represented state machines for describing systems.     

Minimal privacy authorization in web services collaboration

With the popularity of Internet technology, web services are becoming the most promising paradigm for distributed computing. This increased use of web services has meant that more and more personal information of consumers is being shared with web service providers, leading to the need to guarantee that the private data of consumers are not illegitimate collected, used and disclosed in services collaboration. This paper studies how to realize the minimal privacy authorization while achieving the functional goals. Initially, this paper uses authorization policies to specify the privacy privileges of the services collaboration, and utilizes the trust relationships among services to make authorization decision. Next, it models the interface behaviors of services by extending the interface automata to support privacy semantics. Furthermore, it quantitatively analyzes the minimum set of privacy privileges which are required by the services to achieve the functional goals, and presents the minimal authorization algorithm, which helps us to automatically derive optimal authorization policies for a services collaboration. Finally, it verifies the correctness and efficiency of the approach proposed by this paper through a case study.     

Web Services在远程售票系统票券打印中的应用

分析了现有的远程售票系统中基于Socket的票券打印的方案，阐述了其局限性，提出了基于Web Services的解决方案。系统介绍了Web Services的关键技术，并描述了实际应用中完整的实现过程，包括创建、保护、调用Web Service和在客户端精确控制打印等。