Implementing calendars and temporal rules in next generation databases

In applications like financial trading, scheduling, manufacturing and process control, time based predicates in queries and rules are very important. There is also a need to define lists of time points or intervals. The authors refer to these lists as calendars. The authors present a system of calendars that allow specification of natural-language time-based expressions, maintenance of valid time in databases, specification of temporal conditions in database queries and rules, and user-defined semantics for date manipulation. A simple list based language is proposed to define, manipulate and query calendars. The design of the parser and an algorithm for efficient 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