摘要
本文在文[1][2][3]的基础上讨论了不完全关系模式的有关分解问题。由于不完全关系含有多种函数依赖保持,使得不完全关系中各属性间的依赖关系变得复杂并具有动态特性。因此,在模式分解中应给出一种新的分解理论和方法,以解决空值带来的问题。为此,本文讨论了空值环境下的候选关键字、投影、连接等问题,提出了把含有确定候选关键字的不完全关系模式无损连接分解成含有空值的2NF 及判定算法。
On the basis of literatures [1] [2] [3],the problem of incomplete relational schema
decompositions is discussed.Since incomplete relations contain many kinds of functional dependency
holds,these kinds of functional dependency holds cause the dependent relations among attributes in
incomplete relations to be complicated and have dynamic properties.Therefore a new decomposi-
tion theory and method should be given in schema decomposition in order to solve the problems bring-
ing from null values.So the problems of candidate keys,projection and join under null value circ-
umstances are discussed in this paper.And the method to decomposit incomplete relational schema con-
taining definite candidate keys into 2NF with null values with lcssless joins and its decision algorithm
are proposed.
出处
《计算机研究与发展》
EI
CSCD
北大核心
1991年第8期16-23,共8页
Journal of Computer Research and Development
