SQL语句的自动生成

通过分析开发数据库应用程序过程中应用SQL语句存在的问题,提出了SQL语句自动生成技术的思想。给出了自动生成SQL语句的设计思路和实现步骤并具体设计了所用到的过程和函数。     

一种实现数据库同态计算的ELGamal重加密算法

数据库加密技术旨在解决数据库隐私数据泄露问题.现有的关于加密数据库的研究应用未实现或仅部分实现密文数据的同态计算功能,使得SQL查询语句在加密数据库中无法高效执行甚至失效.提出一种实现数据库同态计算的ELGamal重加密算法,该算法基于ELGamal乘法同态密码体制和数据库外层加密方式,通过将SQL查询语句中算术表达式重写为具有同态计算的重加密表达式,实现数据库基于密文进行同态计算的目标.本文提出的ELGamal重加密算法在DDH问题是困难的假设下可以抵抗选择明文攻击.     

关系数据库细粒度访问控制设计与实现

通过扩展SQL语句支持关系数据库细粒度访问控制(FGAC)策略的描述,扩展的SQL语句同时支持封闭式细粒度访问控制策略和开放式细粒度访问控制策略的描述,即支持细粒度的否定授权.给出了基于查询改写思想的动态查询改写算法,实现了细粒度访问控制,同时给出了细粒度访问控制实现框架,并在数据库管理系统(DBMS)中实现.实验验证了该实现方法的可行性.     

浅谈ASP与SQL数据库连接的实现

论述了ASP和SQL的工作原理，分析了ASP与SQL数据库连接的实现过程。从标准语句及例句两方面介绍了实现ASP与SQL数据库连接的基本语法过程。     

决策树中ID3算法的研究

ID3算法是决策树分类方法的核心算法,文章论述了ID3算法的基本思想和实现方法,并对ID3算法的性能进行分析,发现该算法存在不足之处.针对ID3算法倾向于多属性值的缺点,引入了权值对算法进行改进,并通过试验对改进前后的算法进行比较,结果表明改进后的算法是有效的.     

基于ALPHA语言的复杂查询SQL语句生成

用SQL语言表达复杂查询,是数据库教学中的一个重点和难点,但对数据库理论的初学者是个挑战。文章提出了一个复杂查询的SQL语句生成框架,首先将复杂查询用ALPHA语言表示,然后利用逻辑谓词等价变换理论,将ALPHA语句中的全称量词和逻辑蕴含进行等价变换,再使用ALPHA语言向SQL语言变换生成算法生成SQL查询。该框架在多年的教学实践中得到了检验,并取得了较好的教学效果。     

用SQL语句实现关系代数运算探讨

SQL语句用法及关系代数运算是数据库原理课中的重点和难点内容,关系代数是一种抽象数学语言,是关系数据操纵语言的一种传统表达方式.SQL是业界公认的一种结构化的查询语言,虽然各类数据库管理系统中SQL语言有不同语法结构,但差别不大,且已形成了关系数据库的国际标准语言,本文只探讨如何用SQL语句来实现关系代数的运算,从而加深学生对SQL语句的用法和对关系代数运算的理解.     

办公自动化系统与管理信息系统的集成技术

阐述了办公自动化(OA)系统与管理信息系统之间的集成技术。以SQL数据库作为后台数据库,通过在notes中调用SQL语句实现二者之间的数据集成,实现了Domino数据库和Sybase/Oracle等关系型数据库的数据信息的交互。     

XML数据在关系数据库中存储和检索和研究和实现

论述了关系型数据库和XML数据之间的相互转换，给出了将XML数据存储在关系数据库和将存储在关系数据库的XML数据恢复的XML形式的算法，由于实际数据类型的复杂性，使用Schema来定义XML文档类型，试验结果表明算法具有较好的性能，讨论了将XML＿QL查询语句转换为SQL查询语句的设计，根据文中XML数据存储在关系型数据库中的算法，可以对XML＿QL查询语句的语法，语义进行分析以转换为相应形式的SQL语句来关系数据库中查询被存储的XML数据，并返回相应的结果集。     

基于Oracle数据库SQL查询语句优化规则的研究

通过对Oracle数据库中SQL查询语句的执行原理和过程进行研究,以现有系统书号实名申领信息系统中的数据库为例,对执行的SQL查询语句的执行计划进行了分析,从SQL语句执行过程涉及到的系统资源和执行方式入手,对SQL查询语句进行优化,最后得出一系列的优化规则,并根据优化结果对这些规则进行验证。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to