摘要
在关系数据库理论中 ,称恰满足给定函数依赖集及其闭包的关系为Armstrong关系。R .Fagin、C .Beeri等在 [1,2 ]中研究了Armstrong关系 ,给出了存在性证明、判定充要条件及几个应用 ,却没有给出Armstrong关系的构造算法。本文首先讨论了一类特殊的属性子集———闭属性集 ,即与其闭包相等的属性子集 ,给出了这类属性集的判定充要定理及一些性质 ,证明了关系模式上所有闭属性集族的最小生成子族的存在唯一性 ,最后给出了一个基于最小生成子族的Armstrong关系的构造算法 ,弥补了 [1,2
In the theory of relational database,a relation which satisfies precisely a given set of functional dependencies and its closure is called as Armstrong relation [1,2] .In references[1,2],R.Fagin and C.Beeri et al.have given the proof of the existence of these special relations,obtained a necessary and sufficient judgement theorem,and induced several important results,nevertheless they have not shown the constructing algorithm for Armstrong relations.This paper discusses first a special kind of attribute sets——closed attribute sets,which are equal to their closure,and then gives a necessary and sufficient judgement theorem and some properties for them,proves the existence and uniqueness of the minimal generating subset of all closed set on a relational schema.Based on the minimal generating subset,an algorithm for constructing Armstrong relation is given at last,which supplements the constructing algorithm not shown in references[1,2]
出处
《计算机应用与软件》
CSCD
北大核心
2004年第6期72-75,共4页
Computer Applications and Software
