具有全序时态类型集时态函数依赖集的研究

Study on Set of Temporal Functional Dependencies with Totally Ordered Set of Temporal Types

好的数据库逻辑设计目标是消除数据冗余以及插入、删除和更新异常.对于时态数据库,可以通过具有多时间粒度的时态函数依赖(TFDs)约束对时态数模式进行规范化.但是由于时间维的引入和多时间粒度的使用而给数据库设计带来巨大的复杂性.一般来说,系统所能处理的和相当多的应用所涉及到的时态类型集满足全序关系,并且具有全序时态类型集的TFD集的推导规则与传统函数依赖(FDs)的Armstrong公理有着紧密的联系.通过分析TFDs与FDs之间存在的联系,利用传统FD集的相应算法,提出了成员籍、有限属性闭包等TFD集的一些重要算法.这些算法是时态数据库进一步规范化的基础.

The purpose of good database logical design is to eliminate data redundancy and insertion, deletion and update anomalies. For temporal databases, temporal schemes may be normalized by using constraints of temporal functional dependencies (TFDs) with multiple temporal granularities. However, the adoption of temporal dimension and usage of multiple temporal granularities make it very complicated to design a temporal database. Generally, the set of temporal types that can be processed by a system and involved in lots of applications, meet totally ordered relation, and the set of TFDs with a totally ordered set of temporal types is closely related to the Armstrong axioms of traditional functional dependencies (FDs). By analyzing the existing relationships between TFDs and FDs and utilizing corresponding algorithms for traditional set of FDs, some important algorithms such as membership and finite closure of attributes algorithms are proposed for given set of TFDs. These algorithms are the basis of further normalization for temporal databases.