试论数据库设计的基本原则

讨论数据库设计中产生的数据冗余和更新异常的问题及原因并进行了用表谓词来描述表含义的方法，最后提出了数据库设计中的基本原则，作为避免数据冗余和更新异常的有效方法。     

排课系统中数据库表的设计

数据库表是数据库中所必需要设计的内容,表结构是否规范直接关系到后续数据的保持,这就要求建立一个简洁、清晰的数据库表,以免存储冗余信息,造成浪费。     

关系数据库模式的研究

数据库模式会直接影响和决定数据的完整性、准确性和一致性。规范化理论为数据库的设计提供了理论指南和工具,在设计数据库时,必须结合应用环境和实际情况合理的选择数据库的规范模式,才能做到既消除数据冗余和操作异常,又减少额外开销。     

分布式环境中数据库模式设计实践

近年来,数据规模呈爆炸式增长,使得传统集中式数据库难以满足业务需求.而分布式数据库可以将数据存储在多个节点上,具有更好的扩展性,从而可以支撑业务的不断增长.目前,许多企业已经开发出了成功的分布式数据库产品,例如Google Spanner、淘宝的OceanBase等.传统数据库模式设计中,三大范式(1NF、2NF和3NF)及其扩展范式能够减少数据冗余和更新异常,并保证数据的完整性.然而,在分布式架构下,严格遵循范式的模式设计可能带来查询效率较低等问题,而使用反范式模式设计方法通常可以有效提高查询效率.OceanBase是淘宝自主研发的分布式数据库,支持跨行跨表事务,并在OLTP中具有良好的性能,但是对于OLAP业务,其性能并不高.本文将以OceanBase为例,介绍如何利用反范式设计分布式数据库模式,以改善OLAP的查询性能,并通过在OceanBase上部署TPC-H基准评测验证了反范式模式设计的有效性和高效性.     

分布式数据库同步更新的实现方法

把分支机构的数据库作为出版者和分发者,把上级中心的数据库作为订阅者,首先在分发者数据库中对表建立快照代理、日志阅读代理、分发代理．和存储过程的复制事物,并在数据库中记录同步状态信息,然后分发者连接出版者,阅读出版物的事务日志,搜索出带有复制标志的INSERT、UPDATE、DELETE语句和其他更新事务提交给订阅者．当分支机构数据发生更新,日志读取代理即时将更新信息推到上级单位中心的数据库中,实现分发者和订阅者数据库数据两者数据的一致性,从而实现分布式数据库数据的同步更新。     

一种网络冗余流量消除算法

针对大量数据片段冗余传输造成网络带宽浪费严重的问题,提出了一种基于动态查找表的冗余流量消除(DYNATABLE)算法。该算法动态统计流量中以不同字节值开头的数据块的冗余率,在保证目标块抽样率的情况下,选取冗余率高的数据块的首字节值为标识,实时更新查找表,根据查找表中的标识从数据包中选出数据块,对已经传输过的冗余数据块进行简单编码,用编码数据替换原冗余数据片段,再对消除冗余流量的数据包进行传输。对比基于最大值选择和基于静态查找表选择等冗余流量消除算法,DYNATABLE算法能跟踪网络数据的动态变化,带来更高的字节节省,平均字节节省率提高到21.8%。     

基于MD5的可逆无冗余加密算法

直接采用MD5算法对数据库中的敏感数据加密时,合法用户进行查询、更新等操作需要还原数据,MD5算法无法解密数据.可逆的加密算法都需要保存密钥,数据库增加了数据的冗余.本文提出一种基于MD5算法的可逆无冗余算法,实现对数据库中敏感数据进行加密、解密,而且不需要保存密钥.     

基于均匀设计的特征选择方法

针对模式识别系统中有效特征的选择问题,采用支持向量机作为分类器,提出了基于均匀设计的特征选择方法．根据均匀设计表的结构及采用的数据集进行训练、测试,最后检验所选的特征子集．实验结果表明,该方法能够有效地去除数据集的冗余特征,取得比使用特征全集更好的分类性能．     

PowerBuilder数据窗口多表更新的通用性方法

PowerBuilder中单数据窗口只能更新一个表,目前常用的解决方法是编写函数实现基于单数据窗口的两表更新,当表的数目增加时又需要重新编程或重复调用函数.为克服该局限性,对其进行了改进,通过建立全局函数实现单数据窗口的多表更新,提高了代码的可重用性和可维护性,通过向函数传递不同的参数,使程序不必受制于数据库表的个数和名称,体现其通用性,从而使PowerBuilder应用程序的报表更新技术更完善,更灵活.     

分布式数据库在公路建设项目管理中的应用

在分析分布式数据库对公路建设项目管理的优越特性基础上，提出了公路建设项目管理的分布数据库，其中包括数据分割和冗余问题的解决、并发控制机制设计、系统结构设计和查询处理．     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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