Maintaining data temporal consistency in distributed real-time systems

Previous works on maintaining temporal consistency of real-time data objects mainly focuses on real-time database systems in which the transmission delays (jitters) of update jobs are simply ignored. However, this assumption does not hold in distributed real-time systems where the jitters of the update jobs can be large and change unpredictably with time. In this paper, we examine the design problems when the More-Less (ML) approach (Xiong and Ramamritham in Proc. of the IEEE real-time systems symposium 1999; IEEE Trans Comput 53:567?C583, 2004), known to be an efficient scheme for maintaining temporal consistency of real-time data objects, is applied in a distributed real-time system environment. We propose two new extensions based on ML, called Jitter-based More-Less (JB-ML) and Statistical Jitter-based More-Less (SJB-ML) to address the jitter problems. JB-ML assumes that in the system the jitter is a constant for each update task, and it provides a deterministic guarantee in temporal consistency of the real-time data objects. SJB-ML further relaxes this restriction and provides a statistical guarantee based on the given QoS requirements of the real-time data objects. We demonstrate through extensive simulation experiments that both JB-ML and SJB-ML are effective approaches and they significantly outperform ML in terms of improving schedulability.     

A pessimistic consistency control algorithm for replicated fileswhich achieves high availability

A consistency control algorithm is described for managing replicated files in the face of network partitioning due to node or communication link failures. It adopts a pessimistic approach in that mutual consistency among copies of a file is maintained by permitting files to be accessed only in a single partition at any given time. The algorithm simplifies the Davcev-Burkhard dynamic voting algorithm (1985) and also improves its availability by adding the notion of linearly ordered copies. A proof that any pessimistic algorithm with fresh reads is one-copy serializable is given     

Maintaining consistency in a replicated software archive

Archives of software packages made available on the Internet have become an increasingly common and important way of distributing these resources. To improve local access speeds, it is common for these archives to be mirrored, i.e. replicated at regional sites throughout the world. When these sites are also active participants in the augmentation and maintenance of the archive, it becomes necessary to impose a regime which will ensure that errors and inconsistencies do not arise as a result of conflicting activities at different centres. We describe here procedures which have been developed for the organisation and management of a multi-site software archive in which items of software may be introduced or updated at any of the participating sites. A simple algorithm is outlined to propagate changes made to all sites, protecting against conflicting changes and ensuring consistency of the archive is maintained. Similar methods are applicable to the management of other kinds of distributed system, especially internet-based information services, including World Wide Web sites which allow regional updates. © 1998 John Wiley & Sons, Ltd.     

复杂开发环境中设计文档的一致性维护

在复杂软件开发过程中会产生各种类型的文档。不同的开发工具通常会使用不同的方法来存储这些文档数据,因此很难保证这些文档及文档间的一致性。为了解决这个问题,本文应用XML技术设计并实现了一个用于管理这些设计文档的系统,重点使用XML查询语言来对这些数据的一致性进行约束和检查。由于系统本身的轻量级和灵活性,可以适应不同工程的需求并且可以在基于网络的分布式环境中加以整合。     

Maintaining mobile transactional consistency in hybrid broadcast environments

Recently there have been attempts in several research areas at efficiently utilizing the resources of mobile computers. Considering the properties in mobile computing environments, push-based data dissemination systems have lately attracted considerable attention. However, skewed access patterns among mobile clients makes response time worse, and they prefer to send data requests to the server explicitly through an uplink channel. A broadcast supporting an uplink channel is called a hybrid broadcast. In this paper, we devise new transaction processing algorithms for hybrid broadcasts. It is assumed that data objects that the server maintains are divided into Push_Data for periodic broadcasting and Pull_Data for on-demand service. That is, clients have to explicitly request data objects in Pull_Data. Maintaining transactional consistency in this environment without much additional cost is our main concern. Finally, we evaluate performance behavior through simulation study.Received: 15 November 2002, Published online: 5 August 2004This work was done as part of the Information & Communication Fundamental Technology Research Program, supported by the Ministry of Information & Communication in the Republic of Korea.     

Dynamic consistency of fuzzy conditional temporal problems

Conditional Temporal Problems (CTPs) can deal simultaneously with uncertainty and temporal constraints, allowing for the representation of temporal and conditional plans. CTPPs generalize CTPs by adding preferences to the temporal constraints and by allowing fuzzy thresholds for the occurrence of some events. Here we focus on dynamic consistency of CTPPs, the most useful notion of consistency in practice. We describe an algorithm which allows for testing if a CTPP is dynamically consistent and we study its complexity. Simple temporal problems with preferences and uncertainty (STPPUs) are another formalism to model temporal constraints where preference and uncertainty coexist. While uncertainty is CTPPs is modeled via conditions on the execution of variables, in STPPUs it is modelled by means of events whose occurrence time is not known. We consider the relation between CTPPs and STPPUs and we show that the former framework is at least as expressive as the second one. Such a result is obtained by providing a polynomial mapping from STPPUs to CTPPs.     

Optimistic versus pessimistic concurrency control mechanisms in database management systems

Concurrency control mechanisms are necessary to preserve database integrity in a multi-user environment. Two kinds of concurrency control mechanisms are considered in this paper, namely optimistic and pessimistic ones. Optimistic concurrency control is based on the idea of conflicts and transaction restart while pessimistic concurrency control uses locking as the basic serialization mechanism. Analytic and simulation models of both mechanisms were developed in order to compare them as far as transaction response time is concerned. These results take into consideration parameters such as transaction arrival rate, number of database resources accessed per transaction, size of the database, system processing rate and degree of multiprogramming.     

On earliest deadline first scheduling for temporal consistency maintenance

A real-time object is one whose state may become invalid with the passage of time. A temporal validity interval is associated with the object state, and the real-time object is temporally consistent if its temporal validity interval has not expired. Clearly, the problem of maintaining temporal consistency of data is motivated by the need for a real-time system to track its environment correctly. Hence, sensor transactions must be able to execute periodically and also each instance of a transaction should perform the relevant data update before its deadline. Unfortunately, the period and deadline assignment problem for periodic sensor transactions has not received the attention that it deserves. An exception is the More-Less scheme, which uses the Deadline Monotonic (DM) algorithm for scheduling periodic sensor transactions. However, there is no work addressing this problem from the perspective of dynamic priority scheduling. In this paper, we examine the problem of temporal consistency maintenance using the Earliest Deadline First (EDF) algorithm in three steps: First, the problem is transformed to another problem with a sufficient (but not necessary) condition for feasibly assigning periods and deadlines. An optimal solution for the problem can be found in linear time, and the resulting processor utilization is characterized and compared to a traditional approach. Second, an algorithm to search for the optimal periods and deadlines is proposed. The problem can be solved for sensor transactions that require any arbitrary deadlines. However, the optimal algorithm does not scale well when the problem size increases. Hence, thirdly, we propose a heuristic search-based algorithm that is more efficient than the optimal algorithm and is capable of finding a solution if one exists.

Maintaining consistency between CAD elements in collaborative design using association management and propagation

The complete definition of a product often requires the collaboration of various partners. Data sharing and exchange between partners has thus become an important task throughout a product's entire life cycle. Even while subsets of the product definition are exchanged (as work packages) and modified by various partners, the global product definition must remain consistent. This paper focuses on maintaining consistency between Computer-Aided Design (CAD) work packages and the global product Digital Mock-Up (DMU). The approach is designed to ensure better management of the associations between objects when a work package is extracted from the global DMU, modified by a partner, sent back to the originator and then re-inserted into the global DMU, which must be modified in turn so as to maintain consistency. To this end, we propose an association management model for the digital mock-up (Digital Mock-up Association Management Model, DMU-AMM) that transposes the associations that exist between a DMU and a work package, including package extraction and modifications, to ultimately guide the evolution of the DMU so as to reconcile the associations between a modified DMU and the modified work package and there by maintain consistency.     

复制式协同图形编辑环境中复合Undo操作语义一致性维护研究*

复制式架构下的二维CAD协同图形编辑环境中,用户界面所发出的Undo操作从语义上讲是针对复合操作本身的,但传统的一致性维护算法是基于原子操作的,对Undo操作的支持也是以原子操作为单位的,这样就会导致复合Undo操作的语义不一致性问题。分析了CAD图形编辑环境中复合操作的类型及Undo操作的执行前提,讨论了Undo操作存在的情况下的冲突定义,提出了基于版本分裂机制的冲突解决策略,并描述了复合Undo操作在本地和远程站点的执行流程及主要算法。最后通过实例分析证明了该方法的有效性。     

Resolving actuator redundancy—optimal control vs. control allocation

This paper considers actuator redundancy management for a class of overactuated nonlinear systems. Two tools for distributing the control effort among a redundant set of actuators are optimal control design and control allocation. In this paper, we investigate the relationship between these two design tools when the performance indexes are quadratic in the control input. We show that for a particular class of nonlinear systems, they give exactly the same design freedom in distributing the control effort among the actuators. Linear quadratic optimal control is contained as a special case. A benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.     

Dynamical consistency in hierarchical supervisory control

A hierarchical control theory is presented founded upon the trace-dynamical consistency property, which is an extension of the notion of dynamical consistency (DC) to the supervisory case of automata with disablable transitions. Partitions of a system state space are considered for which both the trace-DC and the (non-blocking) in-block controllability (IBC) conditions hold; it is shown that low-level non-blocking controllable languages project up to such languages in the high-level system, and that, when the (non-blocking) IBC condition also holds, high-level non-blocking controllable languages map down to such languages in the low-level system. It is demonstrated that the resulting pairs of low-level and high-level languages satisfy a version of the hierarchical consistency condition found in the existing language-based hierarchical supervisory control theory. The structures produced in the formulation of hierarchical control in this paper permit efficient regulator design (and, in particular, repeated re-design) for hierarchy-compatible language specifications; such specifications consist of low-level languages whose maximal controllable sublanguages are realizable by a combination of a high-level (possibly history-dependent) regulator and a set of (state-dependent) low-level regulators (specified block-wise). An algorithm is proposed which facilitates the construction of (non-blocking) IBC partitions of systems with vocalized states. Examples are presented, including a material transfer line with re-entrant flow and a double queue     

Quality of service guarantee for temporal consistency of real-time transactions

The more-less (ML) scheme has been shown to be an efficient approach for maintaining temporal consistency of real-time data objects. Although ML provides a deterministic guarantee in temporal consistency, the number of update transactions that can be supported in a system is limited. This is due to its use of the worst-case computation time in deriving deadlines and periods of update transactions. This paper studies the problem of temporal consistency maintenance where a certain degree of temporal inconsistency is tolerable. A suite of statistical more-less (SML) approaches are proposed to explore the trade-off between quality of service (QoS) of temporal consistency and the number of supported transactions. It begins with a baseline algorithm, SML-BA, which provides the requested QoS of temporal consistency. Then, SML with optimization (SML-OPT) is proposed to further improve the QoS by better utilizing the excess processor capacity. Finally, SML-OPT is enhanced with a slack reclaiming scheme (SML-SR). The reclaimed slacks are used to process jobs whose required computation time is larger than the guaranteed computation time. Simulation experiments are conducted to compare the performance of these schemes (SML-BA, SML-OPT, and SML-SR) together with the deterministic more-less and half-half schemes. The results show that the SML schemes are effective in trading the schedulability of transactions for the QoS guaranteed. Moreover, SML-SR performs best and offers a significant QoS improvement over SML-BA and SML-OPT.     

The integration of scheduling and control: Top-down vs. bottom-up

The flexible operation of continuous processes often requires the integration of scheduling and control. This can be achieved by top-down or bottom-up approaches. We compare the two paradigms in-silico using an air separation unit as a benchmark process. To demonstrate the top-down paradigm, we identify data-driven models of the closed-loop process dynamics based on a mechanistic model and use them in scheduling calculations that are performed offline. The resulting target trajectories are passed to a linear model predictive control (LMPC) system and implemented in the process. To demonstrate the bottom-up paradigm, we define an economic nonlinear model predictive control (eNMPC) scheme, which performs dynamic optimization using the full model in closed-loop to directly obtain the control variable profiles to be implemented in the process. We provide implementations of the process model equations as both a gPROMS and a Modelica model to encourage future comparison of approaches for flexible operation, process control, and/or handling disturbances. The performance, advantages, and disadvantages of the two strategies are analyzed using demand-response scenarios with varying levels of fluctuations in electricity prices, as well as considering the cases of known, instantaneous, and completely unknown load changes. The similarities and differences of the two approaches as relevant to flexible operation of continuous processes are discussed. Integrated scheduling and control leverages existing infrastructure and can be immediately applied to real operation tasks. Both operation strategies achieve successful process operation with remarkable economic improvements (up to 8%) compared to constant operation. eNMPC requires more computational resources, and is – at the moment – not implementable in real-time due to maximum optimization times exceeding the controller sampling time. However, eNMPC achieves up to 2.5 times higher operating cost savings compared to the top-down approach, owing in part to the more accurate modeling of key process dynamics.     

Imposing temporal consistency on deep monocular body shape and pose estimation

Computational Visual Media - Accurate and temporally consistent modeling of human bodies is essential for a wide range of applications, including character animation, understanding human social...     

Necessary conditions for control consistency in hierarchical control of discrete-event systems

Hierarchical consistency is an important concept in control theory of hierarchical discrete-event systems (DESs). In order to establish corresponding control structure in high level, Wong introduced (1990, 1994) the concept of control consistency, which implies hierarchical consistency. However, to check whether a hierarchical DES is control consistent is computationally expensive. In this note, we try to reduce the computational complexity. At first, the kernel condition of control consistency is divided into three simpler parts and computational complexity is analyzed. Further discussion is made to obtain some new necessary conditions for control consistency, by which one can easily verify whether a hierarchical DES is not control consistent.     

A hierarchical consistency framework for real-time supervisory control

The control framework of hierarchical consistency of timed discrete-event systems (TDES’s) is investigated in a standard two-level hierarchy. Real-time concepts and the associated theoretical results supporting consistent TDES hierarchies are developed. Where the given low-level system model of the hierarchy possesses time fidelity, a consistency version that assures time fidelity of the high-level system model is also developed. Importantly, this version furnishes a sound real-time high-level specification design foundation for hierarchical control. An example illustrates the new time-fidelity control foundation. Given that in general, a given two-level TDES hierarchy is not hierarchically consistent between the levels, the structural existence and synthesis of the sufficiency structure for hierarchical consistency is investigated. Both the timed versions of hierarchical consistency - without and with output-time fidelity guarantee - are successively treated. The abstraction or output-system refinement procedures for the version without output-time fidelity guarantee are first developed for a class of TDES hierarchies under mild output-system design restrictions. The abstraction methods for the version with output-time fidelity are then developed for a subclass ‘linearly’ structured under further output-system design restrictions. A detailed example explains and illustrates the use of an overarching method developed.     

多刚体系统的一致性控制研究

基于非自治级联系统理论,以非完整移动机器人为研究对象,研究多刚体系统的一致性问题,提出了一种新的分布式控制器。通过引入持续激励扰动项,验证了无论参考信号是否为持续激励信号,所提出的控制器都能实现系统一致性的目的,且能一致到期望的参考值。利用李雅普诺夫方法对系统进行了稳定性分析。最后,对所提控制器进行数值仿真,结果验证了所提出的控制器的有效性。     

Spacecraft coordination control in 6DOF: Integrator backstepping vs passivity-based control

In this paper, we present three nonlinear control solutions for 6DOF spacecraft formation control, adopted from Euler-Lagrange system theory. The quaternion parametrization results in dual equilibrium points in the closed loop system, and the controllers are proved to render these uniformly asymptotically stable. We also present a theoretical comparison of the three control solutions, together with simulation results to visualize the performance of the controllers.