移动实时数据库的时间一致性研究

在实际应用中,实时的移动数据库系统不仅需要确保事务完成的最后期限,而且还需保证事务处理的时态一致性,为此研究了移动实时数据库的时间一致性.从移动实时数据库时间特性的定义出发,分析实时事务的时间一致性限制因素,提出实时事务的时间一致性维护策略.性能测试结果表明,乐观协议OPT-Wait与基于锁的协议VL-HP各有优劣,在延误截止时间率方面,OPT-Wait协议比VL-HP协议性能好.     

一种基于QoS的事务工作流并发调度算法

并发冲突引起的连锁夭折会降低系统性能,提出了一种基于QoS的事务工作流调度算法,该算法适应异构环境需求,支持基于QoS的延迟调度优化策略和SAFE集合扩充优化策略,可根据QoS参数调整相应的调度决策,在保证分布异构环境中复杂事务工作流并发正确性的同时减少连锁夭折.证明了算法不会引起循环等待和饿死现象,可保证调度的可串行性和可恢复性,性能模拟表明该算法适用于长期运行的事务工作流的并发调度,可有效减少连锁夭折,从而减少由此带来的性能损失.     

CORBA对象事务服务及其并发控制研究

为有效地保证分布式事务的ACID性质以及解决多个客户程序并发访问某一事务所造成的访问冲突,根据CORBA对象事务服务OTS(Object Transaction Service)、并发控制服务CCS(Concurrency Control service)及其提供的相关接口,采用两步提交协议和并发控制锁机制实现.并将两者相结合实现一个账户之间的转账操作,证明其可行性.     

工业控制系统的实时数据库设计

分析了工业控制系统的实时数据库的特点和需求 ,通过与普通数据库的比较 ,从数据模型、存储结构和介质、存取方式和途径以及完整性和一致性的维护等角度分析了实时数据库的设计方法。     

并发系统中实时数据处理

介绍了在并发系统中对实时数据快速处理的方法。设计中采用的各种技术为实时处理高密度、大流量的数据提供了一种高效、可行的解决方案。     

确保时态一致性的实时并发控制协议

实时控制系统通常需要维护大量的时态数据对象,这些时态数据对象是现实世界不断变化的物理环境的逻辑表示.应用事务通过对时态数据对象的访问来产生最终的控制活动.在实际应用中,实时控制系统不仅需要确保事务能在规定的期限内完成,也需要保证事务存取的是时态一致性的数据对象.传统的实时并发控制协议强调事务截止期的满足,而忽略了事务对其所存取数据对象有时态一致性需求.本文首先给出了数据和事务时态一致性的形式化定义,在此基础上,提出了一种新的能确保时态一致性的实时并发控制协议:时态一致性高优先级两段锁协议(TCHP-2PL).为了实现更好的实时性能,我们对TCHP-2PL进行了改进,通过引入相似性概念,提出了TCHP-2PL的改进版本:STCHP-2PL.性能测试结果显示,STCHP-2PL在确保时态一致性的同时仍能保证很好的实时性能.     

基于并发事务逻辑的Web服务编制验证

 服务编制解决的是组织之间的业务集成问题,面临的是一个广泛分布、动态、自治、异构的网络环境,保障组合服务的正确执行以及相关特性的验证问题显得尤为重要.形式化方法是一种有效的解决方法,服务编制需要建立在严格的形式化模型的基础上,可以通过具有明确的、形式化语义的形式化模型研制验证工具来完成组合服务正确性的验证.本文基于并发事务逻辑(CTR:Concurrent TRansaction Logic)对服务编制的元素进行了描述和建模,给出了从WS-BPEL到并发事务逻辑的转换规则,讨论了服务编制在CTR中的验证问题以及WS-BPEL和CTR的表达能力,最后给出了一个实际的服务编制在CTR中建模的例子,验证了服务编制的CTR模型的有效性.     

一种高可靠性移动通信网络数据库的实现模式

移动通信网络数据库需要提供高可靠性、实时性的电信级服务,传统的关系型数据库管理系统无法满足这一具有事务限时响应的实时性应用。该文以移动通信网中位置寄存器HLR的应用为例,提出了一种实时数据库与商用数据库相结合的实现模式,用以提供大客量大事务处理能力和电信级高实时性响应的服务,并从事务的访问分配分流策略、事务的并发控制、数据的一致性等方面分析了系统的高可靠性和可用性。     

Research on concurrency control algorithm for real-time collaborative editing systems

Real-time collaborative editing systems are important groupware tools in the computer supported cooperative work (CSCW) field. They support geographically dispersed users to edit shared files, graphics, etc. simultaneously. Currently popular real-time collaborative editing systems mostly use plain text data for edit and synchronization, and the corresponding operations are deleting, adding or modifying characters. The data acquisition system's metadata in this article is the module, such as deleting, adding or modifying a certain question. On the basis of differential synchronization algorithms and generic operation transformation (GOT) algorithm, this paper proposes a new concurrency control algorithm differential synchronization and generic operation transformation control algorithm (DSGOT).     

On real-time databases: concurrency control and scheduling

In addition to maintaining database consistency as in conventional databases, real-time database systems must also handle transactions with timing constraints. While transaction response time and throughput are usually used to measure a conventional database system, the percentage of transactions satisfying the deadlines or a time-critical value function is often used to evaluate a real-time database system. Scheduling real-time transactions is far more complex than traditional real-time scheduling in the sense that (1) worst case execution times are typically hard to estimate, since not only CPU but also I/O requirement is involved; and (2) certain aspects of concurrency control may not integrate well with real-time scheduling. In this paper, we first develop a taxonomy of the underlying design space of concurrency control including the various techniques for achieving serializability and improving performance. This taxonomy provides us with a foundation for addressing the real-time issues. We then consider the integration of concurrency control with real-time requirements. The implications of using run policies to better utilize real-time scheduling in a database environment are examined. Finally, as timing constraints may be more important than data consistency in certain hard realtime database applications, we also discuss several approaches that explore the nonserializable semantics of real-time transactions to meet the hard deadlines     

An adaptive switching learning control method for trajectory tracking of robot manipulators

In this paper, a new adaptive switching learning control approach, called adaptive switching learning PD control (ASL-PD), is proposed for trajectory tracking of robot manipulators in an iterative operation mode. The ASL-PD control method is a combination of the feedback PD control law with a gain switching technique and the feedforward learning control law with the input torque profile. The torque profile is updated by the previous torque profile (which makes sense for learning). Furthermore, in this new control method, the switching control scheme is integrated into the iterative learning procedure; as such, the trajectory tracking converges very fast. The ASL-PD method achieves the asymptotical convergence based on the Lyapunov’s method. The ASL-PD method possesses both adaptive and learning capabilities with a simple control structure. The simulation study validates this new method. In particular, both position and velocity tracking errors monotonically decrease with the increase of the number of iterations. The convergence rate with the ASL-PD method is faster than that of the adaptive iterative learning control method proposed by others in literature.     

一种不依赖状态估计的自适应输出反馈控制方法

研究了一种不依赖状态估计的自适应输出反馈控制方法。首先引入伪控制信号使系统反馈线性化，然后设计一个线性动态补偿器和在线神经网络，自适应消除不确定性和建模所引起的误差。对一含有末建模动态的非线性系统的仿真结果表明，该控制方法能够消除系统的稳态误差，提高系统动态性能，并且具有较好的鲁棒性。     

一种智能交通系统的自适应拥塞控制方法

针对突发性车流量自适应调整主通道流量控制,提出多相位路口实时的自适应拥塞控制算法,提高系统管理算法在突发性车流状况中的适应能力,以两种信息通道实现车流队列管理的控制与学习功能,并结合参考模型机制实现模糊反向推理算法。仿真实验结果表明,该控制方案能改善实际交通状况,控制效果优于定时控制的方法,提高平面交通路口的通行能力50%以上。     

自适应MPAM解调方法研究

提出了一种新型的基于自适应滤波器权系数解调多进制幅度调制(MPAM)信号的方法.文中以常用的最小均方误差自适应算法(LMS)为例,讨论了新型的MPAM自适应解调的过程及其性能.该解调算法不需要自适应滤波器完成收敛,从而降低了采样频率和处理速度.给出的理论性能与仿真结果表明,MPAM自适应解调的误码率仿真结果与理论值吻合非常好;而且该方法具有抗干扰性能强、输出响应快、便于数字信号处理(DSP)技术实现等特点,在相同的采样频率下其误码率优于相关解调的误码率.     

A dynamic and integrated concurrency control for distributeddatabases

An integrated approach to concurrency control adaptively allows classical pessimistic (two-phase locking) or optimistic (using certification) approaches. The principles for a distributed integrated method controlling both locking and optimistic transactions are defined. The implementation of these principles leads to a method for constructing the serialization order of transactions, using their conflicts. This dynamic construction prevents the systematic rejection of old (long) readers, as in the multiversion methods. On the other hand, applying Thomas' rule to control the write conflicts permits the presence of old (long) writers     

An adaptive pulse-width control loop

Clock distribution and generation circuitry forms a critical component of current synchronous digital systems. Digital system clocks must not only have low jitter and low skew, but also a well-controlled duty cycle in order to facilitate versatile clocking techniques. In high-speed complementary metal oxide semiconductor (CMOS) clock buffer design, the duty cycle of a clock is liable to be changed when the clock passes through a multistage buffer because the circuit is not pure digital (Fenghao and Svensson 2000 Fenghao, M and Svensson, C. 2000. Pulsewidth control loop in high-speed CMOS clock buffers. IEEE Journal of Solid-State Circuits, 35: 134–141.  [Google Scholar]). In this paper, we propose a pulsewidth control loop referred as adaptive pulsewidth control loop (APWCL) that adopts the same architecture as the conventional PWCL, but with two modifications. The first one relates to implementation of the pseudo inverter control stage (PICS), while the second to involvement of adaptive control loop. The first modification provides generation of output pulses during all APWCL's modes of operation and the second faster locking time. For 1.2?μm double-metal double-poly CMOS process with V_dd ?=?5?V and operating frequency of 100?MHz, results of SPICE simulation show that the duty cycle can be well controlled in the range from 20% up to 80% if the loop parameters are properly chosen.     

立体图像视差自适应调整算法

针对不同尺寸立体显示器播放立体视频时立体视觉效果存在的差异,提出一种通过调节图像水平视差改善立体显示效果的方法。首先应用立体匹配算法得到立体图像初始视差,通过图像分割与连通性检测从中可靠地获取水平视差范围;为保证图像中全部景物在舒适立体融像区内成像,根据显示器尺寸与观看距离,调整左右眼图像在原立体视频中相对位置,形成合理的水平视差,从而在立体显示器上产生舒适的立体视觉效果。实验证明,本文提出的方法可自适应地调整立体图像的水平视差并较好地改善立体显示效果。     

An adaptive real-time ECG compression algorithm with variable threshold

A real-time compression algorithm has been developed which is suitable for both real-time ECG (electrocardiogram) transmission and ECG data storing. The algorithm represents a modification of the amplitude zone time epoch coding (AZTEC) technique extended with several statistical parameters used to calculate the variable threshold. The proposed algorithm has been applied in the design of a pacemaker followup system for the online ECG data transmission from the pacemaker implanted in a human being to the computer system located at the clinic.<>