LOGICAL DESIGN FOR TEMPORAL DATABASES WITH MULTIPLE GRANULARITIES

The purpose of good database logical design is to eliminate data redun dancy and insertion and deletion anomalies. In order to achieve this o bjective for temporal databases, the notions of temporal types, which formalize time granularities, and temporal functional dependencies (TF Ds) are introduced. A temporal type is a monotonic mapping from ticks of time (represented by positive integers) to time sets (represented b y subsets of reaIs) and is used to capture various standard and user-d efined calendars. A TFD is a proper extension of the traditional funct ional dependency and takes the form X -->(mu) Y, meaning that there is a unique value for Y during one tick of the temporal type mu for one particular X value. An axiomatization for TFDs is given. Because a fin ite set of TFDs usually implies an infinite number of TFDs, we introdu ce the notion of and give an axiomatization for a finite closure to ef fectively capture a finite set of implied TFDs that are essential to t he logical design. Temporal normalization procedures with respect to T FDs are given. Specifically, temporal Boyce-Codd normal form (TBCNF) t hat avoids all data redundancies due to TFDs, and temporal third norma l form (T3NF) that allows dependency preservation, are defined. Both n ormal forms are proper extensions of their traditional counterparts, B CNF and 3NF. Decomposition algorithms are presented that give lossless TBCNF decompositions and lossless, dependency-preserving, T3NF decomp ositions.