Logical Design for Temporal Databases with Multiple Granularities

ing with credit is permitted. To copy otherwise, to republish, to Post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Publications Dept, ACM Inc., fax +1 (212) 869-0481, or permissions@acm.org. 2 \Delta Wang, Bettini, Brodsky, Jajodia George Mason University The purpose of good database logical design is to eliminate data redundancy and insertion and deletion anomalies. In order to achieve this objective for temporal databases, the notions of temporal types, which formalize time granularities, and temporal functional dependencies (TFDs) are introduced. A temporal type is a monotonic mapping from ticks of time (represented by positive integers) to time sets (represented by subsets of reals) and is used to capture various standard and user-defined calendars. A TFD is a proper extension of the traditional functional dependency and takes the form X \Gamma! ¯ Y , meaning that there is a unique value for Y during one tick..