一种面向公有链的轻量级可扩展技术

区块链技术解决了在不可信环境下建立信任的基础难题,被视为继云计算、物联网和人工智能之后的又一项颠覆性技术.然而,目前公有链面临2大根本难题：1)较低的系统吞吐率无法满足大规模运用的需求;2)持续增长的账本和状态数据,对节点磁盘和内存容量提出了较高要求.已有的扩容技术往往只针对提升系统吞吐,忽略了区块链数据增长对节点存储资源消耗的严重问题.为此,提出了PocketChain,一种对存储友好的轻量级扩容技术,在不牺牲去中心化与安全性的前提下,实现高吞吐和低存储的特性.首先,针对数据增长问题,PocketChain采用无状态客户端设计,使用RSA累加器对状态进行压缩,使得验证节点只需存储区块头部信息,大大降低节点对磁盘和内存的需求.其次,PocketChain将无状态客户端运用于分片技术架构下,在提升系统吞吐的同时,克服分片周期性随机重组导致的状态迁移问题,从而能进一步提升分片重组频率,增加分片系统安全性.实验结果表明:该方法能够有效降低节点存储需求,并线性提升系统吞吐.     

Scalable Network Management Using Lightweight Programmable Network Services

  Although the Simple Network Management Protocol (SNMP) has proven to be a powerful tool for network administrators, it is widely accepted that SNMP does not offer the scalability or the functionality needed to manage large systems of routers and end systems. Active/programmable networks and mobile agent systems have been proposed as alternative network management solutions, offering new functionality and better scalability. Unfortunately, the flexibility and programmability of these (heavyweight) systems comes with its own set of problems, which has prevented them from becoming widely adopted.This paper presents an ultra-lightweight programmable network service called ephemeral state processing (ESP) that can be used to efficiently monitor and collect information from large-scale networks. Although the service offers a limited set of features, the building blocks it does offer can be combined in novel ways to solve a wide range of network management problems while avoiding the problems that plague (heavyweight) active network approaches. The simplicity of ESP allows us to make it available as a general-purpose service that can be used by all packets in the network. We demonstrate the utility of the service by showing how it can be used to efficiently solve common network management problems.

A Scalable Testing Framework for Location-Based Services

A novel testing framework for location based services is introduced. In particular, the paper showcases a novel architecture for such a framework. The implementation of the framework illustrates both the functionality and the feasibility of the framework proposed and the utility of the architecture. The new framework is evaluated through comparison to several other methodologies currently available for the testing of location-based applications. A case study is presented in which the testing framework was applied to a typical mobile service tracking system. It is concluded that the proposed testing framework achieves the best coverage of the entire location based service testing problem of the currently available methodologies; being equipped to test the widest array of application attributes and allowing for the automation of testing activities.     

Coordination Algorithm for Distributed Testing

With the emergence of new models, architectures and middleware such as ODP, TINA and CORBA, for developing open distributed systems, testing technology requires adaptation for use within conformance assessment in such systems. All these frameworks are object-based and aim at creating open distributed environments supporting interworking, interoperability, and portability, in spite of heterogeneity and autonomy of the related systems. In this context, an open distributed system may be viewed as a system providing standardized distributed interfaces for interacting with other systems. Conformance of such a system can be assessed by attaching a related tester at each provided interface. However, many problems of controllability and observability influencing fault detection during the testing process, arise if there is no coordination between the testers. In this paper, we show how to cope with these problems by using test coordination procedures in a distributed testing architecture.     

基于轻量级容器架构DAO层可重复性单元测试

单元测试的出现给程序员的编程工作带来了乐趣,更多的程序员希望能进行深入实践.但在对单元测试更加全面深入的使用过程中,却遇到了越来越多的障碍.随着B/S架构的流行,轻量级容器架构的J2EE模式是大多数项目的首选,并在此基础上使用DAO(数据访问对象)模式与数据库层进行交互.数据库中的数据会在使用过程中变得不稳定,会使得测试代码变得不具可重复性.而单元测试最重要的特性就是可重复性,文中探讨的就是关于DAO层的单元测试的可重复性.经过在实际项目中的认真实践得出了可行的方法,现作简要介绍.DAO层的单元测试的依赖于数据库中的数据,实现单元测试的可重复性需要对于每次单元测试执行时数据库的数据都是符合要求的.可从两方面保证数据库中的数据符合要求:一是启动每轮单元测试时提供符合要求的数据;二是对于那些会破坏数据库状态的单元测试在结束时均执行一个恢复操作,将数据库恢复到原来的状态.     

基于双重覆盖信息协同的协议模糊测试

模糊测试在挖掘协议软件安全漏洞、提高安全性方面发挥着巨大的作用. 近年来将状态引入服务端程序模糊测试受到广泛关注. 本文针对现有方法未充分利用协议模糊测试过程信息、无法持续关注重点状态, 导致模糊测试效率较低的问题, 提出了基于双重覆盖信息协同的协议模糊测试方法. 首先, 本文提出的状态选择算法, 通过建立状态空间到程序空间的映射, 利用启发式的计算方法为每个状态设置权重, 以引导模糊测试持续关注更可能存在缺陷的状态. 其次, 快速探测种子不影响状态但改变程序覆盖的位置, 并限制变异位置以充分测试重点状态对应的代码区域. 本文在基线工具AFLNet和SnapFuzz上验证了改进算法的有效性, 并最终集成实现了协议模糊测试工具C2SFuzz. 对LightFTP、Live555等协议服务端程序最新版进行了实验后, 发现5个未知的漏洞.     

Coordination of multiagent systems through explicit valuation of action

The effectiveness of a system relates to its ability to fulfill its functional requirements. When a system consists of a set of collaborating agents, the overall performance may depend more on their ability to work together than on optimizing individual behavior. In fact, the goal of an agent is often at odds with the interest of the collective. The limitations of centralized control for complex systems suggest the need for decentralized coordination. This can be achieved by having each agent take explicit account of the cost of engaging in an activity as well as a measure of reward for effective behavior. The consideration of payoffs and penalties leads to an economic perspective of multiagent systems. In consequence, it is possible to draw on previous work in diverse fields, ranging from game theory to welfare economics and social policy. The promise and limitations of the explicit valuation approach are examined. To illustrate, the behavior of collaborative systems can be interpreted in terms of games of strategy; this approach permits a better understanding of the conditions for globally optimal behavior, as well as strategies for their attainment. The notions of agents and explicit valuation of action are versatile concepts. One indication of the versatility lies in the fact that these concepts cover as a special case the idea of genetic algorithms as a mechanism for learning systems.     

Trust in Distributed Teams: Support through Continuous Coordination

In this article we report on our investigation of trust in distributed development teams and the role that software tools can play in supporting teams. Our investigation shows that the continuous coordination paradigm tools Palantir, Ariadne, World View, and Workspace Activity Viewer help distributed teams develop trust by sharing information across boundaries through visualizations and in other ways. Our analysis provides insights into the role existing tools can play in developing trust and how future tools can promote trust.     

Debugging and Testing Optimizers through Comparison Checking

We present a novel technique called comparison checking that helps optimizer writers debug optimizers by testing, for given inputs, that the semantics of a program are not changed by the application of optimizations. We have successfully applied comparison checking to a large class of program transformations that alter (1) the relative ordering in which values are computed by the intermediate code statements, (2) the form of the intermediate code statements, and (3) the control flow structure using code replication. We outline the key steps that lead to the automation of comparison checking. The application of comparison checking to test the implementations of high level loop transformations, low level code optimizations, and global register allocation for given program inputs is then described.     

Real time query propagation strategies with Lightweight Coordination Calculus (LCC) for ad hoc networks of geospatial databases

Large volumes of geospatial data are increasingly made available through dynamic networks, such as ad hoc networks. Consequently, new adapted query propagation approaches that take into account geospatial aspects of data are needed. Different existing query propagation approaches use various criteria to select relevant sources. In addition, many approaches rely on existing semantic mappings between sources; however, in ad hoc networks, sources move autonomously and in a dynamic fashion. Our goal is rather to reduce the number of sources that must be accessed to answer a query and, therefore, to reduce the volume of semantic mappings that needs to be computed to answer the query. In this paper, we propose three real time query propagation strategies to address this issue. Those strategies reproduce the behavior of members of a social network. The strategies are designed to be part of a real time semantic interoperability framework for ad hoc networks of geospatial databases. The strategies have been formalized with the Lightweight Coordination Calculus (LCC), which support distributed interactions based on social norms and constraints. The implementation and testing of the strategies show that they complement each other to provide optimal query answers.     

Formal Specification and Enactment of Security Policies through Agent Coordination Contexts

Our research moves from three fundamental considerations that concern the modelling and engineering of complex systems. First, organization, coordination and security are strictly related issues that should be modelled in a uniform and coherent framework. Second, models, technologies and methodologies should come hand in hand, so that abstractions used in the analysis and design stages should be still “alive and kicking” at development and execution time. Third, the general non-formalisability of complex systems should not prevent us from using formal tools whenever useful, such as in proving or ensuring properties of limited but meaningful portions of a system.By focussing on multi-agent systems, we discuss the notion of Agent Coordination Context (ACC) as an abstraction that (i) works as an organization and security abstraction, (ii) integrates well with abstractions provided by coordination infrastructures, and (iii) covers the engineering process from design to deployment. In particular, in this paper we study the syntax and semantics of a language for ACCs specification, exploiting typical process algebra techniques. Accordingly, we show that process algebras are a suitable tool for both specification and enactment of security and coordination policies through ACCs.     

Testing of MEMS capacitive accelerometer structure through electro-static actuation

The present paper discusses a method for testing a MEMS capacitive accelerometer structure through electrical actuation. The response of a standard MEMS capacitive accelerometer structure for different electrical actuation voltages has been analyzed. The accelerometer structure along with a capacitance sensing integrated circuit (IC) MS3110 is modeled and simulated. A set of proto-type accelerometer structures is fabricated and packaged in PGA packages. The packaged MEMS structures and MS3110 IC are integrated on a printed circuit board. The MEMS structure is actuated by applying the electrical signal through the actuation fingers and the change in capacitance is measured by the MS3110 IC. The simulated and measured results show some interesting phenomenon like dipping and frequency doubling which are useful for initial testing and characterization of a MEMS accelerometer structure.     

Testing input validation in Web applications through automated model recovery

Input validation is essential and critical in Web applications. It is the enforcement of constraints that any input must satisfy before it is accepted to raise external effects. We have discovered some empirical properties for characterizing input validation in Web applications. In this paper, we propose an approach for automated recovery of input validation model from program source code. The model recovered is represented in a variant of control flow graph, called validation flow graph, which shows essential input validation features implemented in programs. Based on the model, we then formulate two coverage criteria for testing input validation. The two criteria can be used to guide the structural testing of input validation in Web applications. We have evaluated the proposed approach through case studies and experiments.     

Testing the random walk hypothesis through robust estimation of correlation

This paper uses Monte Carlo simulations to examine the properties of the conventional Pearson and some of the most well-known robust to outliers estimators of correlation in the presence of general heteroskedasticity. We show that the tests of a random walk based on the Pearson autocorrelation coefficient, including the Lo and MacKinlay [1988. Stock market prices do not follow random walks: evidence from a simple specification test. Rev. Financial Studies 1, 41-66] robust form of the variance-ratio test, can be unreliable in the presence of some forms of conditional heteroskedasticity. As an alternative to the Pearson autocorrelation coefficient, we propose the median coefficient of autocorrelation. Our simulation results show that, in contrast to the Pearson autocorrelation coefficient, the median coefficient of autocorrelation is robust to conditional heteroskedasticity. When applied to exchange rate returns, the variance-ratio test based on the median autocorrelation coefficient provides stronger evidence against the random walk hypothesis compared with the Lo and MacKinlay [1988. Stock market prices do not follow random walks: evidence from a simple specification test. Rev. Financial Studies 1, 41-66] robust variance-ratio test.     

Model-based Kernel Testing for Concurrency Bugs through Counter Example Replay

Despite the growing need for customized operating system kernels for embedded devices, kernel development continues to suffer from high development and testing costs for several reasons, including the high complexity of the kernel code, the infeasibility of unit testing, exponential numbers of concurrent behaviors, and a lack of proper tool support. To alleviate these difficulties, this study proposes the MOdel-based KERnel Testing (MOKERT) framework, which supports detection of concurrency bugs in the kernel by combining both model checking techniques and testing methods. The MOKERT framework was applied to the file systems of the Linux 2.6 kernel and found a data race bug in the proc file system.     

Semiconcurrent Online Testing of Transition Faults through Output Response Comparison of Identical Circuits

We describe a method for online testing of delay faults based on the comparison of output responses of identical circuits. The method allows one of the circuits to participate in useful computations during the testing process, while the other circuit must be idle. We refer to this method as semiconcurrent online testing. While unknown input vectors are applied to the circuit that participates in useful computations, the proposed method applies modified vectors to the idle circuit. In this way, different conditions are created for the detection of delay faults, allowing identical delay faults that affect both circuits to be detected. In designing the modified vectors, we ensure that the expected fault-free responses of the two circuits are identical. We also ensure that the hardware for modifying the vectors applied to the idle circuit will be easy to implement on-chip.     

Getting acquainted through social network sites: Testing a model of online uncertainty reduction and social attraction

The first aim of this study was to examine which uncertainty reduction strategies members of social network sites used to gain information about a person who they had recently met online. The second aim was to investigate whether and how these uncertainty reduction strategies resulted in social attraction. Drawing on a survey of 704 members of a social network site, we found that respondents had used active, passive, and interactive strategies to reduce uncertainty about their new acquaintance. Interactive strategies were most effective in reducing uncertainty about the target person. Respondents’ level of uncertainty about the acquaintance mediated the relationships between the use of interactive uncertainty strategies and perceived similarity on the one hand and social attraction on the other. Finally, respondents’ perceived valence of the obtained information about the acquaintance moderated the relationship between the level of uncertainty and social attraction.