基于MapReduce的连续概率Skyline查询

大数据对传统的Skyline研究产生了挑战,利用并行框架MapReduce计算大数据下的Skyline已成为一个研究热点。研究了不确定移动对象的Skyline查询问题,提出了一种MapReduce框架下基于事件跟踪的连续概率Skyline查询算法——MR-DTrack(domination-track algorithm based on MapReduce)。首先采用基于角度的划分方法保证负载均衡,通过预计算获取Skyline集可能变化的时刻,在Reduce阶段获取候选概率Skyline集;然后利用局部过滤点剪枝,减少计算开销;最后合并计算出全局概率Skyline集。在人工数据集和真实数据集上的实验验证了算法的有效性。     

基于MapReduce的Skyline查询处理算法

Skyline查询是一个典型的多目标优化查询,在多目标优化、数据挖掘等领域有着广泛的应用。现有的Skyline查询处理算法大都假定数据集存放在单一数据库服务器中,查询处理算法通常也被设计成针对单一服务器的串行算法。随着数据量的急剧增长,特别是在大数据背景下,传统的基于单机的串行Skyline算法已经远远不能满足用户的需求。基于流行的分布式并行编程框架MapReduce,研究了适用于大数据集的并行Skyline查询算法。针对影响MapReduce计算的因素,对现有基于角度的划分策略进行了改进,提出了Balanced Angular划分策略;同时,为了减少Reduce过程的计算量,提出了在Map端预先进行数据过滤的策略。实验结果显示所提出的Skyline查询算法能显著提升系统性能。     

RDF数据的Skyline优化查询

为解决海量RDF数据的Skyline查询问题,通过分析现有Skyline查询算法的优缺点,提出一种针对海量RDF数据的查询机制。对RDF数据的存储结构进行分析,根据RDF数据垂直存储结构,设计一种候选Skyline点筛选策略,提前修剪部分非Skyline元组,减少Skyline支配点计算的数据量;在筛选的基础上,给出基于MapReduce的Skyline并行化查询算法。实验结果表明,提前筛选能有效减小查询的数据集,并行化算法能够有效提高查询的效率。     

高效多子空间Skyline查询处理算法

随着Skyline查询应用的增多,子空间Skyline查询成为热点。针对实际应用中用户从多角度审视某一数据集的需求,充分研究了多子空间Skyline查询问题。在分析现有子空间Skyline查询算法解决该问题不足的基础上,提出了子空间立方体群(subspace skycube group,SSG)结构,并给出了基于该结构的同时计算任意多个子空间Skyline查询的MSSC(multiple subspace skycube)算法。该算法采用子空间候选集(subspace candidate sets,SCS),并充分利用了子空间立方体群结构中各子空间Skyline结果间的共享关系;在此基础上,算法采用求和过滤以及最大值过滤等方法,对数据集进行剪枝和过滤,从而进一步提高算法效率。最后,分别用人造数据和真实数据对算法进行实验,并与现有算法进行比较,结果表明MSSC算法可以高效地解决多子空间Skyline查询问题。     

3FO:基于过滤的一种Skyline查询算法

Skyline查询是从一个给定的数据集上返回所有不被其它点支配的点的集合.本文主要针对二维和三维空间上Skyline查询结果的单调性特点提出了一种新的3FO算法,它通过NN过滤、最小值覆盖过滤和单调性过滤三次过滤操作,删除非skyline点数据.可以快速地返回全部的Skyline点.实验结果表明,该算法比传统算法在相同数据集上平均性能提高2-3倍,是一种高效的算法.     

基于高维空间的在线高效子空间Skyline算法——CSky

Skyline计算是要发现数据集中不被其他点支配的所有点的集合.近来,它在实时在线服务方面的良好应用前景,使其成为数据库研究领域的一个热点.实际应用中,用户通常期望快速、渐进地返回Skyline计算结果,因此文中主要讨论了高维空间子空间Skyline渐进查询问题.据我们所知,现有的Skyline计算方法都不能直接或者通过简单修改来高效解决该种查询问题.BNL(Blocked Nested Loop)算法是一个可用来进行子空间Skyline计算的算法,但是,该方法低效且非渐进.基于此,文中提出了在线高效子空间Skyline算法--CSky(Count the Skyline).该算法充分利用了一个新颖数据结构--InvertS的特征,即通过对目标数据集进行排序,存放最可能为Skyline点的数据于算法优先扫描的位置,这使得CSky算法能高效计算出任意子空间上的Skyline;同时,CSky每次计算子空间Skyline查询时,至多访问一遍数据库;再有,算法扫描一个点时,只需和当前已发现的Skyline点进行比较即能判断该点是否为Skyline点,保证了算法的渐进性.这样,相比BNL,CSky大大减少了计算开销,具有其他基于索引的Skyline算法计算Skyline时的高效,且这种高效适用于所有子空间.理论分析和实验表明,在解决高维空间子空间Skyline查询问题方面,CSky性能大大优于BNL.     

Mapreduce下改进Skyline的高效算法

目前基于 MapReduce 的 Skyline 算法随着维度增大会陷入维度灾难，不能高效地解决大数据条件下的计算问题。提出高效算法 MRBPS，利用数据间的互不支配特性，通过一个优化轴点对数据集建立区域标识，在 Map 和 Reduce 阶段优先比较每个点的区域标识，将多维比较简化为一维比较，提高了计算效率，通过系统实验证明：此算法在大数据量时能够明显提高计算效率，与现有算法相比具有高效性和可靠性。     

MapReduce框架下的Skyline计算

由于Skyline查询广泛应用于多目标决策、数据可视化等领域,近年来成为数据库领域的一个研究热点。针对云计算环境,在MapReduce框架下设计并实现了Skyline算法。MapReduce是一个运行在大型集群上处理海量数据的并行计算框架,其主要思想是任务的分解与结果的汇总。基于不同的数据划分思想,实施了三种Skyline并行算法,分别是基于MapReduce的块嵌套循环算法(MapReduce based block-nested-loops,MR-BNL)、基于MapReduce的排序过滤算法(MapReduce based sort-filter-skyline,MR-SFS)以及基于MapReduce的位图算法(MapReduce based bitmap,MR-Bitmap),并针对这三种算法进行了系统的实验比较,得出了不同数据分布、维数、缓存等因素对算法性能的影响结果。     

MapReduce框架下的Skyline结果优化算法

随着大数据时代的到来,数据量和数据复杂度急剧提高,Skyline查询结果集规模巨大,无法为用户提供精确的信息.MapReduce作为并行计算框架,已广泛应用于大数据处理中.本文提出了MapReduce框架下基于支配个数的结果优化算法(MR-DMN),解决了大数据环境下的Skyline结果集优化问题.大量的实验表明:算法具有良好的时间和空间效率.     

组合Skyline的求解与更新算法

针对现有组合Skyline查询算法剪枝效率低、对低维数据集计算速度不理想的问题,提出一种快速求解与更新组合Skyline的算法。定义支配区的相关概念,给出相应剪枝规则裁剪无用的数据组合。对于数据集添加数据点和删除数据点的情况,在原有查询结果的基础上根据数据点所在分区实施不同的操作,从而实现查询结果的快速更新。实验结果表明,该算法可有效提高剪枝效率,加快运算速度。     

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