Modeling crontab behavior in SQL (using postgreSQL9.3)

I'd like to store information about periodic events (classroom times) in an PostgreSQL database table. I've looked at ISO 8601 repeating intervals, but that's not quite the same since they are not continuous and back-to-back. But rather might work MWF or just on Saturday and Sunday; honestly in a hundred of arbitrary ways. One way of modeling that behavior that I've thought of is to mimic crontab-like columns in a table. But before I go down that road, is there anything more sophisticated or is there a better tool for that sort of behavior?