closure theorem
1.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]
