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异构数据层基于多关系半连接查询优化算法
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作者 刘宝军 《现代商贸工业》 2010年第24期360-360,共1页
查询效率是异构数据层必须面临的一大挑战,由于普通多关系半连接优化算法,异构数据层缓冲区不能作为查询中间结果的最后装配站点,采用半连接方法优化连接操作,并在半连接的基础上提出了多个站点的半连接执行优化算法,该算法根据半连接... 查询效率是异构数据层必须面临的一大挑战,由于普通多关系半连接优化算法,异构数据层缓冲区不能作为查询中间结果的最后装配站点,采用半连接方法优化连接操作,并在半连接的基础上提出了多个站点的半连接执行优化算法,该算法根据半连接生成有向无序树,使多个半连接操作能够并行执行。结果表明改进的多关系半连接查询优化算法明显减少了中间结果的数据量,有效地降低了网络通信总代价,提高了全局查询效率。 展开更多
关键词 导构数据层 半链接 优化算法
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A Control Scheme Based on Online Delay Evaluation for a Class of Networked Control Systems 被引量:1
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作者 马向华 谢剑英 魏震 《Journal of Donghua University(English Edition)》 EI CAS 2004年第4期124-130,共7页
A control scheme that integrates control technology with communication technology to solve the delay problem is introduced for a class of networked control systems: Networked Half-Link Systems (NHLS). Concretely, we u... A control scheme that integrates control technology with communication technology to solve the delay problem is introduced for a class of networked control systems: Networked Half-Link Systems (NHLS). Concretely, we use the master-slave clock synchronization technology to evaluate the delays online, and then the LQ optimal control based on delays is adopted to stabilize the controlled plant. During the clock synchronization process, the error of evaluated delays is inevitably induced from the clock synchronization error, which will deteriorate the system performances, and even make system unstable in certain cases. Hence, the discussions about the clock error, and the related control analysis and design are also developed. Specifically, we present the sufficient conditions of controller parameters that guarantee the system stability, and a controller design method based on the error of delays is addressed thereafter. The experiments based on a CANbus platform are fulfilled, and the experimental results verify the previous analytic results finally. 展开更多
关键词 Networked Control Systems NCS Networked Half-Link Systems NHLS Clock Synchronization Optimal Control Based on Delays CANbus.
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