函数依赖结构的研究及应用

A Study on the Structure of Functional Dependency and Its Application

本文通过对函数依赖之间相互联系的分析和研究,提出了函数依赖结构的新概念和新理论,并论证了其存在性。这种新概念及其理论为解决数据库设计中的许多问题(如构造数据库模式,求解候选关键字等)提供了新的理论依据。

Data dependency, functional dependency (FD) in particular, is an important subject in the relational database theory. FD is used to study the restricted relationship between attributes. In this paper the relationship between FD's is investigated at a high level and both the concept and theory of the structure of FD are proposed. It has been found that the degree of restriction and of closeness are different in the relationships between FD's in a FD set. Accordingly, the relationships between FD's can be divided into three types, namely, SCR (Strongly Connected Relation), WCR (Weakly Connected Relation) and NCR (Non-Connected Relation). The sufficient and necessary conditions for the classification are given. By employing the new concept, a new approach has been found to the computation or solving of some problems (e. g., finding the candidate key word, decomposing the pattern of relationship, etc.) in the relational database theory. The regular structure in knowledge base can therefore be constructed.