Thinking in Sets of Sets

6 10 2009

Over the summer, I built the Chronos temporal toolkit for Oracle. And for the last while I’ve been porting it to Postgres and working on the documentation.

The SQL standard defines several data types to model instances of times. But rarely does anything happen instantaneously. Often what we need to model is a period of time; for instance an airline flight, a hotel stay, a bus route, an employee’s shift, a doctor’s appointment, a leave request. And yet there is no standard defined to handle this. So instead we use some combination of start and end time, an anchor time and interval, or an anchor time and a number representing seconds, minutes or days. Read the rest of this entry »