物化视图选择中权限因子的设计

物化视图是数据仓库中提高查询效率的有效手段,物化视图的选择一直是数据仓库领域的研究热点.通过研究和实验,提出在物化视图选择中加入权限因子,将各候选视图的权限值纳入算法评价函数的计算中,使最终得到的物化视图集既能面向企业基层提供OLAP查询,又能保证企业决策层OLAP查询的速度.     

NDSMMV——一种多维数据集物化视图动态选择新策略

物化视图的选择策略是数据仓库研究的重要问题之一.通过深入研究提出了一种多维数据集中物化视图动态选择的新策略--NDSMMV,包括候选视图生成算法CVGA、物化视图选择算法IGA、物化视图调整算法MAMV和物化视图动态调整算法DMAMV.CVGA基于多维数据格生成候选视图集,对候选视图数量进行压缩以减少后续算法的视图空间搜索代价和时间复杂度;IGA基于视图查询、视图维护和存储空间三元评价标准在候选视图集上进行物化视图的选择;MAMV基于物化视图选择过程已选视图的收益变化情况对物化视图进行进一步调整以提高查询的响应性能;DMAMV定时地判断查询视图类型分布是否变化来决定是否进行物化视图的动态调整,从而避免了物化视图集的"抖动".理论分析和实验结果表明该策略是有效可行的.     

基于遗传算法的受限物化视图

受限物化视图的选择是当前数据仓库研究的最重要的问题之一,且其是个NP问题。本文通过对视图与查询关系的研究,提出了一种选择物化视图的两阶段算法框架,首先利用候选视图选择算法缩小视图选择的范围,而后利用遗传算法解决受限物化视图的选择问题。     

超市数据仓库中物化视图的选择与调整策略

物化视图选择是数据仓库研究领域的一个重要课题,其选择策略直接影响到数据仓库的查询效率.通过对超市数据仓库的设计及已有研究成果的分析,对物化视图的选择算法做了一些改进,并给出了一种据查询情况的变化动态调整物化视图集的算法.     

基于多维护策略的物化视图选择方法

物化视图是数据仓库环境中提高OLAP查询效率的重要手段，因此，物化视图的选择是数据仓库设计中重要的决策之一。本文提出的物化视图选择方法目标是选择合适的视图进行物化，使得查询处理的总代价和物化视图的维护代价最低，提出了物化视图收益模型，并在此基础上基于视图的多维护策略提出了物化视图选择的方法：基于增量和重计算的物化视图选择算法IRMVS、基于增量策略的物化视图选择算法IMVS和基于重计算策略的物化视图选择算法RMVs和基于增量策略的物化后代视图选择算法IMDVS，理论分析和实验表明这些算法是有效可行的。     

面向查询集覆盖的物化视图选择算法

为了解决大容量物理存储条件下数据仓库的物化视图选择问题,提出一种面向查询集覆盖的物化视图选择算法.首先给出了一些概念和定义,然后从视图集的多维数据格中抽取和裁剪出候选视图集,并定义视图物化的效益模型,最后在存储容量的限制下逐步淘汰收益最小的应答查询的冗余视图,得到覆盖所有查询的最优物化视图集.实验结果表明,该算法在较大物理存储条件下的物化视图选择效率优于以往算法,且能够消除物化视图在应答查询时存在的时延“抖动”现象,应答用户查询的平均时间也大为缩短.     

数据仓库性能优化之索引和物化视图耦合方法

为了进一步提高数据仓库的性能, 通过分析数据仓库中性能优化技术的特点, 提出了索引和物化视图耦合的性能优化技术。通过数据挖掘自动选择候选索引和物化视图, 减少查询的扫描范围; 然后研究在物化视图上建立索引的空间高效存储方法, 以提高查询速率; 最后利用成本模型对耦合情况进行分析, 验证了耦合方法可以极大提高单一索引查询或者物化视图的性能。     

数据仓库中物化视图选择策略

为了提高决策支持和OLAP查询的响应效率,数据仓库多采用物化视图的思想.因此,物化视图的选择策略是数据仓库研究的重要问题之一.其目标是选出一组存储、维护代价与查询代价的总和为最小的物化视图.提出一个以MVPP(multi-view processing plan)为视图选择的搜索空间的物化视图选择新算法--VSMF(views selection base on multi-factor)算法.该算法在存储空间约束下同时实现多查询最优化和视图维护最优化.     

数据仓库物化视图选择的混合算法

物化视图是提高数据仓库的查询响应能力以高效支持决策分析的重要手段，但物化视图集选选择是一个复杂问题。结合启发式算法的快速收敛能力和遗传算法的全局优化能力的两层物化视图求解方案提供了物化视图选择问题求解的可行途径。     

数据仓库中物化视图的选取策略

数据仓库中用存储大量的物化视图来加速OLAP的查询响应，物化视图的选取是数据仓库设计中的一个重要问题。论文提出了一个有效的物化视图选取算法，采用基于数据立方体层次搜索的方式选取视图。经分析与测试表明，该算法取得良好的效果和效率。     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate     

SCIENCE CHINA Information Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate