Re: Timezone database changes

"Trevor Talbot" <quension@gmail.com> writes:
> Neither is the birth certificate.  The recorded, legal time of the
> birth is the one that was written down.  If it doesn't happen to match
> an international notion of current time, that's unfortunate, but it's
> not subject to arbitrary changes later.  Even if it does match, it
> still belongs to a specific time zone.  That's the key semantic point:
> regurgitating that time as anything other than exactly what it was
> entered as is simply not correct.

I'm not convinced about that.  One consideration I think you are failing
to account for is that there is a big difference between past and future
times, at least in terms of what is likely to be the meaning of a
change.  The above reasoning might apply to a past time but I think it's
bogus for a future time.  If the TZ offset for a future time changes,
it's likely because of a DST law change, and we are in Peter's
what-time-is-the-appointment scenario.  A TZ offset for a past time
probably should not change, but if it does, it suggests a retroactive
data correction.  Surely you don't intend to prevent people from fixing
bad data?
        regards, tom lane