I think the fundamental problem here is that the table/entity is incredibly badly named. What kind of contract has only three fields?! This isn't a case of YAGNI; no real-world "contract" is this simple.

It appears to actually be some sort of contract_period or contract_duration, and probably has a link to a real "contract" object somewhere that contains the real meat of the concept. But it's hard to tell what's literal and what's the author trying to simplify the example for us.