Modified distributed snapshots algorithm for protocol stabilization

This paper assesses the use of Chandy and Lamport's distributed snapshots algorithm (DSA) for stabilizing a communication protocol, a special type of distributed system. We show that when a loss of coordination occurs during the distributed execution of the protocol, DSA is not guaranteed to terminate, and therefore it sometimes fails to obtain a global state or snapshot. We propose some modifications to DSA to solve this problem. Finally, we discuss how, in the case of a loss of coordination, the modified algorithm can be used to stabilize a communication protocol, and we assess the suitability of the global state obtained by DSA as a recovery point to be used later in a backward recovery procedure.     

A modified genetic algorithm for distributed scheduling problems

Genetic algorithms (GAs) have been widely applied to the scheduling and sequencing problems due to its applicability to different domains and the capability in obtaining near-optimal results. Many investigated GAs are mainly concentrated on the traditional single factory or single job-shop scheduling problems. However, with the increasing popularity of distributed, or globalized production, the previously used GAs are required to be further explored in order to deal with the newly emerged distributed scheduling problems. In this paper, a modified GA is presented, which is capable of solving traditional scheduling problems as well as distributed scheduling problems. Various scheduling objectives can be achieved including minimizing makespan, cost and weighted multiple criteria. The proposed algorithm has been evaluated with satisfactory results through several classical scheduling benchmarks. Furthermore, the capability of the modified GA was also tested for handling the distributed scheduling problems.     

Verification of distributed control systems in intelligent manufacturing

This paper presents an application of formal methods for validation of flexible manufacturing systems controlled by distributed controllers. A software tool verification environment for distributed applications (VEDA) is developed for modeling and verification of distributed control systems. The tool provides an integrated environment for formal, model-based verification of the execution control of function blocks following the new international standard IEC61499. The modeling is performed in a closed-loop way using manually developed models of plants and automatically generated models of controllers.     

A scheduling algorithm based on the singular value decomposition heuristic method in a distributed manufacturing system

Because distributed manufacturing technology is the foundation of modernized production and traditional heuristic methods exhibit problems of high complexity and low efficiency, this paper designs a scheduling algorithm based on the singular value decomposition heuristic (SVDH) method. The algorithm uses the device distribution and the transportation relationship between devices in a distributed manufacturing system. The algorithm takes the sequence relationship between tasks and the distance between devices as the implicit relationship between the task and the device. The algorithm makes use of the implicit relationship to amend the processing time matrix of the task and corrects the processing time matrix that contains the transportation relationship. Singular value decomposition principal component analysis is performed on the corrected processing time to find the most suitable processing device for each process, and an initial solution matrix is established. The heuristic solution is used to optimize the initial solution to find the optimal scheduling result based on the initial solution matrix. The establishment of the initial solution can effectively reduce the computational complexity of the heuristic solution, realize a parallelizing solution, and improve the efficiency of the heuristic solutions. In addition, the SVDH scheduling result has a lower transfer time between devices due to the consideration of the topology of tasks and devices, that is, the transit time. In this paper, the experiments are conducted on the heuristic performance, scheduling results, and transportation time. The experimental results show the advantages of SVDH over general heuristic algorithms in terms of efficiency and transit time.     

A full sensing window Random-Access algorithm for messages with strict delay constraints

We consider the Channel Multiple-Access problem for messages with strict delay constraints. The constraints are represented by an upper bound on the transmission delays. For this problem, and for binary collision-noncollision feedback per slot, we present a simple full sensing window Random-Access algorithm. We analyze the algorithm and we compute the fraction of maintained traffic and the expected delay for the successfully transmitted packet, for various input Poisson intensities and various values of the bound on the transmission delays.This work was supported by the U.S. Office of Naval Research, under Contract ONR-N14-86-K-0742.     

A distributed task planning system for computer-integrated manufacturing systems

A formal mathematical framework for a distributed task planning method suitable for computerintegrated manufacturing systems is proposed. All pertinent algorithms are derived. A detailed timing analysis associated with primitive actions and activities (complex tasks) execution is presented. A formal language is designed for event tracking and error specification. Based on the derived language, an error recovery mechanism (automaton) is proposed. A case study demonstrates the applicability of the presented method with and without error occurrences.Dr Kokinaki is currently Science and Engineering Research Centre, De Montfort University, UK.     

A partially distributed deadlock detection algorithm

In this paper, a partially distributed deadlock detection algorithm [PDDDA] with multiple outstanding requests is presented for use in distributed database systems. This algorithm allows a process to request many resources simultaneously and uses a central controller for detecting multisite deadlocks. The detection of local deadlocks and the maintenance of local deadlock information are performed at each of the local sites. This partially distributed algorithm alleviates the problem of congestion at the central controller in a centralized algorithm and needs fewer messages and smaller storage space than a fully decentralized algorithm. A set of criteria for comparing deadlock detection algorithms are also given and then used to compare PDDDA with a fully decentralized algorithm proposed by Isloor and Marsland.Research reported herein was supported by US Army CECOM, Ft. Monmouth, New Jersey, under Contract No. DAAB07-83-K-K542. The views, opinions, and/or findings contained in this paper are those of the authors and should not be construed as an official Deportment of the Army position, policy or decision.     

Integration and control of intelligence in distributed manufacturing

The area of intelligent systems has generated a considerable amount of interest—occasionally verging on controversy—within both the research community and the industrial sector. This paper aims to present a unified framework for integrating the methods and techniques related to intelligent systems in the context of design and control of modern manufacturing systems. Particular emphasis is placed on the methodologies relevant to distributed processing over the Internet. Following presentation of a spectrum of intelligent techniques, a framework for integrated analysis of these techniques at different levels in the context of intelligent manufacturing systems is discussed. Integration of methods of artificial intelligence is investigated primarily along two dimensions: the manufacturing product life-cycle dimension, and the organizational complexity dimension. It is shown that at different stages of the product life-cycle, different intelligent and knowledge-oriented techniques are used, mainly because of the varied levels of complexity associated with those stages. Distribution of the system architecture or system control is the most important factor in terms of demanding the use of the most up-to-date distributed intelligence technologies. A tool set for web-enabled design of distributed intelligent systems is presented. Finally, the issue of intelligence control is addressed. It is argued that the dominant criterion according to which the level of intelligence is selected in technological tasks is the required precision of the resulting operation, related to the degree of generalization required by the particular task. The control of knowledge in higher-level tasks has to be executed with a strong involvement of the human component in the feedback loop. In order to facilitate the human intervention, there is a need for readily available, user-transparent computing and telecommunications infrastructure. In its final part, the paper discusses currently emerging ubiquitous systems, which combine this type of infrastructure with new intelligent control systems based on a multi-sensory perception of the state of the controlled process and its environment to give us tools to manage information in a way that would be most natural and easy for the human operator.     

Automated contracting in distributed manufacturing among independent companies

So far, most distributed scheduling systems have been designed for cooperative agents, and are inappropriate for self-interested agents, as for example in inter-firm interactions such as virtual enterprises. This paper discusses issues that arise in extending automated contracting to operate among such self-interested agents. We construct a leveled commitment contracting protocol that allows self-interested agents to efficiently accommodate future events by having the possibility of unilaterally decommitting from a contract based on local reasoning. A decommitment penalty is assigned to both agents in a contract to be freed from the contract, an agent only pays this penalty to the other party. It is formally shown that this leveled commitment feature in a contracting protocol increases Pareto efficiency of deals and can enable contracts by making them individually rational when no full commitment contract can. The analysis is nontrivial because self-interested agents decommit manipulatively a Nash equilibrium analysis of the decommitting game is necessary.     

Divergence control for distributed database systems

This paper presents distributed divergence control algorithms for epsilon serializability for both homogeneous and heterogeneous distributed databases. Epsilon serializability allows for more concurrency by permitting non-serializable interleavings of database operations among epsilon transactions. We first present a strict 2-phase locking divergence control algorithm and an optimistic divergence control algorithm for a homogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction are the same. In such an environment, the total inconsistency of a distributed epsilon transaction is simply the sum of those of all its sub-transactions. We then describe a divergence control algorithm for a heterogeneous distributed database system, where the local orderings of all the sub-transactions of a distributed epsilon transaction may not be the same and the total inconsistency of a distributed epsilon transaction may be greater than the sum of those of all its sub-transactions. As a result, in addition to executing a local divergence control algorithm in each site to maintain the local inconsistency, a global mechanism is needed to take into account the additional inconsistency Recommended by: Meichum Hsu     

HARTEX—a safe real‐time kernel for distributed computer control systems

A hard real‐time kernel is presented for distributed computer control systems (DCCS), highlighting a number of novel features, such as integrated scheduling of hard and soft real‐time tasks as well as tasks and resources; high‐performance time management supporting safe DCCS operation in a hard real‐time environment; synchronization and communication featuring event notification via vector semaphores and transparent communication through implicit (content‐oriented) message addressing. Conventional queues have been substituted by Boolean vectors and vector processing techniques throughout the kernel, resulting in efficient and highly deterministic behaviour, which is characterized by very low overhead and constant execution time of kernel operations, independent of the number of tasks involved. Copyright © 2001 John Wiley & Sons, Ltd.     

分布式检测系统的一种软决策融合算法

在分布式检测系统中,为了进一步提高系统的性能,各传感器可以向融合中心发送多位二进制判决信息.对于这种发送多位判决信息的软决策融合系统,提出了一种对各传感器观测空间进行再划分的方法,它将各传感器的观测空间按照其检测概率和虚警概率进行再划分.这种划分方法能够简化融合中心的计算,且计算机仿真结果表明,应用该方法后融合系统的检测性能有明显的提高.     

分布式控制系统中多种混合任务的容错调度

分布式控制系统中存在有强实时、软实时和非实时等多种实时性的任务,其中强实时任务必须在其时限前完成,否则会出现灾难性后果,因此必须为分布式控制系统提供一定的容错能力。首先给出了用于调度多种实时性任务的单处理器调度算法——双优先级队列调度算法,并分析算法的可调度性条件。针对分布式控制系统,考虑基版本与副版本的执行时间不同时,结合版本复制技术和单处理器调度算法提出了一种新的容错调度算法。分析了算法的可调度行,给出了可任务集的可调度条件判断方法和基版本任务时限的设置方法。在此基础上,采用启发式静态任务分配算法,保证各处理器的负载均衡。本算法在保证任务容错可调度的条件下,可提高系统中各处理器的利用率,仿真结果表明该算法是有效的。     

A query processing algorithm for a system of heterogeneous distributed databases

This paper presents a query processing algorithm, formulated and developed in support of the prototype architecture of the Distributed Access View Integrated Database (DAVID) which is a heterogeneous distributed database management system. The objective of the proposed query processing algorithm is to produce an inexpensive strategy for a given query. The inexpensive query strategy is obtained primarily by computing the most profitable semi-joins and by determining the best sequence of join operations per processing site. The latter is obtained by applying a zero-one integer linear program that uses a non-parametric statistical estimation technique to compute the sizes of the temporary clusters. A cluster is a subset of the cartesian product of a list of atomic and non-atomic domains and is the structure that can represent in a uniform way data stored in relational, hierarchical and network databases.Following some background information on the development of the DAVID prototype, this paper introduces the schema architecture. The schema architecture describes the mechanism by which the component heterogeneous database schemata are mapped into the uniform global schema. This is followed by the formulation of the query processing algorithm, its implementation and an illustration of its use in the context of NASA's Astrophysics Data System.Recommended by: Y. Breitbart     

A decision support algorithm for flexible manufacturing systems control

An application of a modification of Petri nets to mathematical modeling of discrete production processes utilized for a simulation of the flexible manufacturing systems is presented and an algorithm for the support of decision making in the control process of such systems based on the system model analysis is created. The algorithm makes the choice of a suitable control strategy possible in such a way that it automatically generates all potentially possible control strategies, automatically chooses the really possible ones and gives to an operator the chance to choose the most suitable realizable control strategy from the technological point of view.     

伪多跳中继分布式一致性算法

为了提高分布式一致性问题的收敛速度, 减少节点间的通信成本, 本文提出一种分布式一致性算法. 新算法采用单跳通信, 利用非邻接节点的前状态信息进行节点状态更新. 本文证明了在无向通信拓扑下新算法的一致性收敛, 并分析计算了新算法的通信量以及收敛速度的变化. 通过理论分析和仿真验证, 结果表明新算法具有收敛速度快, 通信方式简单, 通信量少, 存在通信延时情况下通信数据不容易丢失等优点.     

支持构件迁移的分布式系统容错算法

随着分布式应用技术的发展,构件的静态性限制了分布式系统在运行期间适应其可用资源变化的要求.为了动态适应系统可用资源,提高系统性能,支持构件可迁移的分布式应用研究受到广泛关注.针对提高构件可迁移分布式应用的可靠性,提出一种分布式系统容错算法.在准同步检查点算法的基础上,通过引入shadow-chain和通讯录机制,实现了构件间通信的可靠性和构件重定位的透明性,从而使得系统能够在较低代价下设置检查点,并能将出错后的系统回卷到一致性状态.