Implementing Calendars and Temporal Rules in Next Generation Databases

In applications like nancial trading, scheduling, manufacturing and process control, time based predicates in queries and rules are very important. There is also a need to de ne sets of time points or intervals. We refer to these sets as calendars. This paper presents a system of calendars that allows speci cation of natural-language time-based expressions, maintenance of valid time in databases, speci cation of temporal conditions in database queries and rules, and user-de ned semantics for date manipulation. A simple set based language is proposed to de ne, manipulate and query calendars. The design of the parser and an algorithm for e cient evaluation of calendar expressions is also described. The paper also describes the implementation of time-based rules in POSTGRES using the proposed system of calendars.