Off by one errors

I received a phone call this morning from my step-mother. It wasn't even 8 AM and I assumed it was bad news, in this case, about my father. No, the flight reservations I had made for them in February had a bug. The conference they were attending ended on 18 Jul which was the date of departure. But they needed to depart on 19 Jul to make that last day of the conference.

I assumed I had gotten it wrong; rather, this departure date was the info she had given me. I know this because she told me today that she had also made the hotel reservations herself for the same (buggy) departure date. I didn't think at the time to ask about this last day. Then, it occurred to me, this is a boundary condition and an off-by-one-error.

Computer science is probably the formal place where I learned about off-by-one-errors. They come in the form of algorithm flaws and most notably crashes or "array bound exceptions."

I suspect these OBO errors are everywhere in life and the way we deal with them is the same way. If we catch them by testing beforehand, we're not lucky, just diligent. Indeed, there's a methodology called "boundary value analysis" for identifying such bugs. Even if we're diligent, we could still be unlucky. That is, we'll get an exception and deal with it in LA and worse, the day of departure.