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     

Applying intelligent agents and semantic web services in eGovernment environments

The increasing volume of eGovernment‐related services is demanding new approaches for service integration and interoperability in this domain. Semantic web (SW) technologies and applications can leverage the potential of eGovernment service integration and discovery, thus tackling the problems of semantic heterogeneity characterizing eGovernment information sources and the different levels of interoperability. eGovernment services will therefore be semantically described in the foreseeable future. In an environment with semantically annotated services, software agents are essential as the entities responsible for exploiting the semantic content in order to automate some tasks, and so enhance the user's experience. In this paper, we present a framework that provides a seamless integration of semantic web services and intelligent agents technologies by making use of ontologies to facilitate their interoperation. The proposed framework can assist in the development of powerful and flexible distributed systems in complex, dynamic, heterogeneous, unpredictable and open environments. Our approach is backed up by a proof‐of‐concept implementation, where the breakthrough of integrating disparate eGovernment services has been tested.     

A prototyping environment for specifying,executing and checking communicating real-time state machines

We describe a toolset, consisting of a graphical editor, a simulator, and an assertion checker, for prototyping real-time systems that are specified as Communicating Real-Time State machines (CRSMs). CRSMs are timed state machines that communicate synchronously over unidirectional channels. The system behavior of CRSMs is characterized by a time-stamped trace of communication events. Safety and timing assertions on the trace of communication events are expressed in a notation based on Real-Time Logic. We illustrate the simulator and assertion checker by specifying a traffic-light controller and other real-time systems. There are two main contributions in this work: first, the prototyping environment serves as a validation of the model, the execution algorithm and paper design of example CRSMs, demonstrating that the ideas are realizable and potentially useful. Secondly, the paper presents a novel and useful method of specifying safety and timing properties, and checking them during simulation.     

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.     

Bandwidth allocation for communicating virtual machines in cloud data centers

The Journal of Supercomputing - High-performance computing in a cloud environment may require massive data transfer among some of the virtual machines (VMs). These VMs are deployed in physical...     

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.     

语义网中基于Web资源本体的数据中介服务

为了搜索Web资源中深层数据并对其利用,在分析利用搜索引擎获取Web资源存在问题的基础上,利用语义网和Web服务技术,提出构建Web资源本体模型实现对Web资源进行语义标识,结合服务管理代理构建数据中介服务应用模型,并以Web服务方式实现Web资源数据中介服务.通过实验验证了Web资源数据中介服务的有效性和可行性,从而实现帮助用户能在形式多样、种类繁多的海量Web资源中有效地荻取和共享Web资源数据.     

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。     

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.