Study On Data Dependency Theory In Temporal Database

The purpose of a good database logical design is to eliminate data redundancy and insertion, deletion and update anomalies. Temporal database is the same case. In this paper, the notions of temporal elementary functional dependency, temporal elementary key, temporal elementary main attribute, temporal simple key and temporal simple main attribute are introduced. On its base, the normalization of temporal database is studied by using constraints of temporal functional dependency(TFD) with multiple time granularities; the concept of temporal elementary key normal form(TEKNF) and temporal simple normal form(TSNF) is introduced; the proof that the normalization degree of both normal form is between T3NF and TBCNF and the normalization degree of TEKNF is lower than that of TSNF are given. Decomposition algorithms that give lossless, dependency_preserving, TEKNF decompositions and lossless, dependency_preserving, TSNF decompositions and the proof for its termination and correction are given. On the base of the process of normalization of relational database, the concepts of temporal multivalued dependency(TMVD) with multiple time granularities based on temporal functional dependency and the theory of multivalued dependency of relational database are introduced. An axiomatization for TMVD is given. Because a finite set of TMVDs usually implies an infinite number of TMVDs, we introduce the notion of and give an axiomation for a finite closure to effectively capture a finite set of implied TMVDs that are essential to the logical design. For temporal scheme with temporal functional dependencies and temporal multivalued dependencies constrains, the usages of multiple time granularities make it more difficult to solve membership problem. However, the solve of membership problem is essential to design an available algorithm of scheme decomposition, thus in this paper, strong close set of set of temporal types, Finite closure of attribution sets, Finite dependency base of attribution sets based on a certain temporal type, Finite dependency base of attribution sets and Special finite dependency base of attribution sets are introduced; the algorithm of Finite closure, Finite dependency base of attribution sets and Special finite dependency base of attribution sets, and the proof for its termination and correction is given. On its base, the algorithm of membership problem and the proof for its termination and correction is given. Finally, Temporal forth normal form with respect to TFDs and TMVDs is given, Decomposition algorithm which is terminal and correct is presented that give lossless T4NF decompositions.