Coordinating context building in heterogeneous information systems

We present an architecture to coordinate the construction of the context within which meaningful information between heterogeneous information systems can be exchanged. We call this coordinator SCOPES (Semantic Coordinator Over Parallel Exploration Spaces). A classification of semantic conflicts we proposed elsewhere is used to build and refine the context, by discovering the semantic mapping rules (inter-schema correspondence assertions) between corresponding elements of the communicating systems. A truth maintenance system is used to manage the multiple intermediate contexts. It provides a mechanism to infer or retract assertions on the basis of the knowledge acquired during the reconciliation process. This nonmonotonic technique is used in conjunction with the Dempster-Shafer theory of belief functions to model the likelihood of alternative contexts. Finally, we propose an algorithm which illustrates how the various components of the architecture interact with one another in order to build context.     

Fully distributed event-triggered asymptotic attitude coordination of multiple spacecraft systems with disturbances

This article studies the leader-following attitude coordination problem of a group of rigid spacecraft subject to communication constraint, disturbances and uncertain control coefficient matrices. A fully distributed adaptive anti-disturbance attitude coordinated control scheme with event-triggering mechanism is developed. First, the event-triggered adaptive distributed observer is designed for each follower to estimate the leader's information without continuous communication requirement. Based on the estimated information, the adaptive anti-disturbance attitude tracking controller is designed such that asymptotic coordinated tracking can be achieved under additive disturbances and actuators' partial loss of efficiency. The proposed control scheme ensures that all the closed-loop signals are bounded and the positive lower bound of inter-event times exists in each subsystem. Simulation results illustrate the effectiveness and flexibility of the proposed control scheme.     

Coordinating Mutually Exclusive Resources using GPGP

Hospital Patient Scheduling is an inherently distributed problem because of the way real hospitals are organized. As medical procedures have become more complex, and their associated tests and treatments have become interrelated, the current ad hoc patient scheduling solutions have been observed to break down. We propose a multi-agent solution using the Generalized Partial Global Planning (GPGP) approach that preserves the existing human organization and authority structures, while providing better system-level performance (increased hospital unit throughput and decreased patient stay time). To do this, we extend GPGP with a new coordination mechanism to handle mutually exclusive resource relationships. Like the other GPGP mechanisms, the new mechanism can be applied to any problem with the appropriate resource relationship. We evaluate this new mechanism in the context of the hospital patient scheduling problem, and examine the effect of increasing interrelations between tasks performed by different hospital units.     

Resource management in open Linda systems

Coordination systems, in particular Linda, have established themselves as important tools for the development of applications to open systems such as the Internet. This paper shows how to tackle a forgotten, but crucial problem in open coordination systems: memory management. As with any system which intends to be of wide use and because memory is a finite resource, coordination systems must address the problems of memory exhaustion. This paper first explores the orthogonality between coordination and computation in order to make it clear that the problem of memory exhaustion in coordination systems cannot be solved using garbage collection schemes implemented at the computation language—a garbage collection scheme must exist in the coordination environment as well. Following the explanation on orthogonality, the paper will focus on describing a garbage collection scheme for the Linda family of coordination systems. It is expected that the solution in Linda can be adapted to other coordination systems as long as they are based on tuple space communication. Copyright © 2003 John Wiley & Sons, Ltd.     

Dimensions of coupling in middleware

It is well accepted that different types of distributed architectures require different degrees of coupling. For example, in client‐server and three‐tier architectures, application components are generally tightly coupled, both with one another and with the underlying middleware. Meanwhile, in off‐line transaction processing, grid computing and mobile applications, the degree of coupling between application components and with the underlying middleware needs to be minimized. Terms such as ‘synchronous’, ‘asynchronous’, ‘blocking’, ‘non‐blocking’, ‘directed’, and ‘non‐directed’ are often used to refer to the degree of coupling required by an architecture or provided by a middleware. However, these terms are used with various connotations. Although various informal definitions have been provided, there is a lack of an overarching formal framework to unambiguously communicate architectural requirements with respect to (de‐)coupling. This article addresses this gap by: (i) formally defining three dimensions of (de‐)coupling; (ii) relating these dimensions to existing middleware; and (iii) proposing notational elements to represent various coupling integration patterns. This article also discusses a prototype that demonstrates the feasibility of its implementation. Copyright © 2009 John Wiley & Sons, Ltd.     

分布式优化的多智能体方法

分布式优化作为分布式协调控制领域中的一个基本而重要的研究课题,近年来,不同领域的众多学者对其产生了广泛的研究兴趣.本文总结归纳了分布式优化的研究现状和近期的研究成果,重点对离线分布式优化和在线分布式优化进行了阐述,并从算法设计和收敛性分析这两个角度进行了剖析.特别地,针对一类混合均衡问题,本文介绍了一类分布式求解算法.最后,阐述了当前尚未解决的问题和未来的研究方向.     

The active components approach for distributed systems development

The development of distributed systems is an intricate task due to inherent characteristics of such systems. In this paper these characteristics are categorised into software engineering, concurrency, distribution and non-functional criteria. Popular classes of distributed systems are classified with respect to these challenges, and it is deduced that modern technological trends lead to the inception of new application classes with increased demands regarding challenges from more than one area. One recent example is the class of ubiquitous computing, which assumes dynamic scenarios in which devices come and go at any time. Furthermore, it is analysed to which extent today's prevailing software development paradigms – object, component, service and agent orientation – are conceptually capable of supporting the challenges. This comparison reveals that each of the paradigms has its own strengths and weaknesses and none addresses all of the challenges. The new active component approach is proposed aiming at a conceptual integration of the existing paradigms in order to tackle all challenges in an intuitive and unified way. The structure, behaviour and composition of active components are explained, and an infrastructure for active components is introduced. To underline the usefulness of the approach real-world applications is presented and an evaluation according to the challenges is given.     

Multi-mode interaction middleware for software services

Due to the independency, variability, and tailorability of software service in the open environment, the research of middleware which supports software services multi-mode interaction is thus of great importance. In this paper, an agent-based multi-mode interaction middleware model and its supporting system for software services were proposed. This model includes an interaction feature decomposition and configuration model to enable interaction programming, an agent-based middleware model, and a programmable coordination media based on reflection technology. The decomposition and configuration model for interaction features can assist programmers in interaction programming by analyzing and synthesizing interaction features. The agent-based middleware model provides a runtime framework for service multi-mode interaction. The programmable coordination media is able to effectively support software service coordination based on multimode interaction. To verify feasibility and efficiency of the above method, the design, implementation and performance analysis of Artemis-M3C, a multi-mode interaction middleware for software services, were introduced. The result shows that the above method is feasible and that the Artemis-M3C system is practical and effective in multi-mode interaction.     

多智能体系统动态协调与分布式控制设计

多智能体系统的主要研究目的在于探索由个体之间的相互作用所产生的群体协调现象的内在机制和原理,而控制或反馈在多智能体协调运动中起着至关重要的作用．本文集中讨论了多智能体协调研究中的几个新兴的基本问题,包括输出调节、集合协调和覆盖．文中着重介绍了分布式估计和内模原理两种多智能体系统分布式输出调节方法及相关的研究进展：关于多智能体系统的目标集合协调,本文从集合聚集和集合优化两方面做了详尽论述：多智能体覆盖有多种分类方式,从覆盖对象的特征出发可将其划分为区域覆盖、边界覆盖和动态目标覆盖3种类型,并对它们的研究背景和最新成果予以介绍．另外文章还对多智能体系统协调控制的理论和应用研究进行了展望．     

面向分布式信息服务平台的协调中间件系统

为了更好地满足用户对分布式信息服务平台的QoS要求，对一个异构的数据库簇进行了研究，提出了基于该簇的一个协调中间件的逻辑模型，并对其设计思想及实现方法进行了详细介绍。该模型将数据的新鲜度引入设计过程，用它作为事务处理的QoS参数来提高系统服务质量。     

Adaptive synchronization control of networked robot systems without velocity measurements

This paper addresses the adaptive synchronization control problem of networked robot systems characterized by the Lagrangian function, where exact dynamic models are unknown and velocity measurements are unavailable. A class of distributed observers, comprised of multiple dynamic variables and static variables, are established based on no a priori restriction on the boundness of the observer states. The observer is compatible for different control schemes with or without structure uncertainties. Using the estimated states given by the observer, adaptive distributed control input is developed, and then, closed‐loop dynamic models for filtered vectors are established. It is proven that our proposed control scheme permits global exact state estimation and global asymptotic synchronization while compensating for structure uncertainties. Simulations are provided to demonstrate the effectiveness of the results.     

Arcademis: a framework for object‐oriented communication middleware development

This paper presents Arcademis, a Java‐based framework for communication middleware development. Arcademis consists of a set of abstract classes, interfaces and concrete components that define the general architecture of middleware systems. Its main objective is to support the implementation of non‐monolithic and easily configurable middleware platforms. Arcademis can be used by middleware developers to deploy systems that meet the requirements of a particular network or technology. Instances of Arcademis can also be customized by distributed systems engineers to meet the requirements of a particular application. For example, new transport protocols, connection management policies, authentication algorithms or invocation semantics can be easily configured in middleware platforms derived from Arcademis. In order to illustrate the use of the framework, the paper describes the RME system, a middleware derived from Arcademis that adds a remote method invocation service to the CLDC configuration of Java 2 Micro Edition (J2ME). Copyright © 2006 John Wiley & Sons, Ltd.     

面向信任的协同模型*

针对开放分布式系统中收集实体的经验值和度量信任困难的现状,采用关注分离的原则,将实体的信任处理行为与计算行为、交互行为进行分离,提出了一个面向信任的协同模型。通过模型中的信任角色实时监听所绑定的计算实体的消息来更新经验值,进而计算信任度,为系统选择相对可信的计算实体提供了依据。最后,利用Java消息服务技术和EJB技术给出了该模型的实现框架。     

事务控制的面向服务系统的动态更新协调

就面向服务的分布式系统中多服务动态更新的协调问题,提出基于事务控制的更新协调策略,包括安全更新时机的选择策略、使用2PC(two-phase-commit)协调多服务更新的控制策略.根据更新实施的各步操作时间开销,提出分别采用更新短事务控制基本更新操作(包括创建服务实例、顺序实施运行时状态转换、重定向服务请求和新服务的...     

多智能体网络系统的自适应协调控制

为实现多智能体网络系统的协调控制,设计了一种新型的带有自适应协调器的控制器.基于动态图建立了多智能体网络系统的模型,并考虑了系统的非线性互联和不可避免存在的时变时滞.应用分布式控制策略,设计了自适应参数估计的协调器,用于调节智能体之间的互联强度,使网络达到稳定的预设水平.并基于Lyapunov-Kra-sovskii泛函和自适应动态偏差反馈控制技术,根据拉萨尔不变集原理证明了偏差控制系统的渐近收敛性.这种控制方法,可在系统参数不确定的情况下,同时完成参数估计和协调控制.所设计的控制律和自适应律简单,易于实现,仿真示例验证了所提方法的有效性.     

Scalable and adaptive log manager in distributed systems

On-line transaction processing (OLTP) systems rely on transaction logging and quorum-based consensus protocol to guarantee durability, high availability and strong consistency. This makes the log manager a key component of distributed database management systems (DDBMSs). The leader of DDBMSs commonly adopts a centralized logging method to writing log entries into a stable storage device and uses a constant log replication strategy to periodically synchronize its state to followers. With the advent of new hardware and high parallelism of transaction processing, the traditional centralized design of logging limits scalability, and the constant trigger condition of replication can not always maintain optimal performance under dynamic workloads. In this paper, we propose a new log manager named Salmo with scalable logging and adaptive replication for distributed database systems. The scalable logging eliminates centralized contention by utilizing a highly concurrent data structure and speedy log hole tracking. The kernel of adaptive replication is an adaptive log shipping method, which dynamically adjusts the number of log entries transmitted between leader and followers based on the real-time workload. We implemented and evaluated Salmo in the open-sourced transaction processing systems Cedar and DBx1000. Experimental results show that Salmo scales well by increasing the number of working threads, improves peak throughput by 1.56\times and reduces latency by more than 4\times over log replication of Raft, and maintains efficient and stable performance under dynamic workloads all the time.     

Distributed adaptive consensus for linear multi-agent systems with quantised information

This paper considers the distributed adaptive consensus problem for linear multi-agent systems with quantised relative information. By using a lemma in algebraic graph theory and introducing a projection operator in adaptive law, a novel distributed adaptive state feedback controller is designed with quantised relative state information. It is shown that the practical consensus for multi-agent systems with a uniform quantiser is achieved via the Lyapunov theory and the non-smooth analysis. In contrast with the existing quantised controllers, which rely on the minimum nonzero eigenvalue of the Laplacian matrix, the developed controller is only dependent on the number of nodes. Furthermore, a dynamic output feedback controller based on quantised relative output information is proposed. Finally, a simulation example is given to illustrate the effectiveness of the proposed control scheme.     

多智能体系统自适应跟踪控制

基于带有非线性动态的二阶多智能体系统,研究了在有动态领导者条件下的跟踪一致性问题。假设跟随者只能获取邻居智能体的相对状态信息,只有一部分跟随者可以获得领导者的位置和速度信息,领导者的控制输入非零且不被任何一个跟随者可知。在通信拓扑为无向连通图的条件下,为了避免全局信息的不确定性,设计了分布式自适应控制协议。将系统的一致性问题转化为误差系统的一致性问题,通过Lyapunov稳定性理论和矩阵理论分析得到了该协议使系统达到一致的充分条件。最后用仿真例子证明了设计方法的有效性。     

Time-varying formation control with attitude synchronization of multiple rigid body systems

In this article, we study the leader-following formation control problem for a group of rigid body systems whose followers' motions are described by dual quaternion equations. A few features are as follows. First, we introduce an exosystem to generate the leader's trajectory as well as the formation configuration, which can produce a large class of time-varying signals so that we can achieve a variety of time-varying formations. Second, to overcome the communication constraint described by a digraph, we extend the distributed observer to estimate not only the desired attitude and angular velocity but also the leader's position and linear velocity. Third, a novel distributed control law is synthesized to furnish a rigorous performance analysis of the closed-loop system. The effectiveness of our design is illustrated by a numerical example.