含空值关系数据库泛关系及其实例的研究  

Research and instance study of universal relations in relational database with null values

作　　者：蒋天发[1] 

机构地区：[1]中南民族大学计算机科学学院,湖北武汉430073

出　　处：《武汉大学学报（工学版）》2004年第6期89-92,共4页Engineering Journal of Wuhan University

基　　金：国家民委重点科研项目资助基金(MZY02004).

摘　　要：在含有空值关系数据库中函数与多值依赖的研究基础上,对含空值关系数据库中泛关系进行了形式化描述和定义;并对传统FD(FunctionalDependency)的传递规则进行了分析研究,得到在约束弱满足意义下不成立结论,提出了含空值关系数据库FD的传递新规则.再对含空值关系数据库中泛实例进行了分析研究,论证了5个引理;在NFD(NullvaluesFunctionalDependency)≠Ω时,从分解R(U)保持PD集,保持合法实例集,相对于NFD有无损连接3个特性一并考虑,得到了分解R(U)5种类型,并对5种类型应用进行了举例讨论.Based on studying the function and multivalue-dependence in relational database with null values, we give a formalized description and definition to the universal relationship. And we find that it's undependable under loose restriction definition after analyzed the rule of traditional functional dependency(FD) transfer, and give a enhanced null-value supported FD transfer rule. In the further analysis of the universal relation in the null-value supported relational database, we proved five lemmas. When NFD(Nullvalues Functional Dependency)≠Ω, we keep fare consideration to disassemble R(U)with holding PD set; holding legitimate instances set; and reduce the damage of relations that relative to NFD, and we get five kinds of style of R(U)disassociation. We also offer the instances and analysis of instances.

关 键 词：空值 关系数据库 泛关系假设 函数依赖 实例 

分 类 号：TP392[自动化与计算机技术—计算机应用技术]