[tz] Non-valid timezones, is there a rule to remove them?

Patrice Scattolin patrice.scattolin at oracle.com
Thu Jan 23 14:08:23 UTC 2014

Even though the rule currently in effect now is identical to a 
neighboring some, that doesn't invalidate the first zone. The main 
reason is for scheduling purposes where, going back in the past for 
example, the difference is now a matter of historical record and needs 
to be kept for software that care for such things such as calendars.

For example, if your are in Argentina/San_Juan and your calendar has a 
meeting in the past (for legal reasons you are keeping track of your 
meetings) where the zones were different, the rule is still in force. 
Were the Argentina/San_Juan removed that meeting time would then move by 
1h when applying Argentina/Buenos Aires in place.

This is more obvious if you have a meeting where some attendees were in 
Argentina/Buenos Aires and some were Argentina/San_Juan. In that case, 
with the old timezone the meeting (say a conference call) occured at two 
different wall clock hours with the old rule (as it actually happened at 
the time) vs with the Argentina/Buenos Aires rule in place forces both 
meeting to have not occured at the same wall clock hours. The UTC never 
changed, just the wallclock but that's what we need the tzid to get 
right. If the meeting occured around midnight, it could even change day 
for some attendees!

So to maintain historical accuracy the old rule cannot be taken out.

On 23/01/2014 5:40 AM, Fabiano Fidêncio wrote:
>     Sorry, that makes no sense.  How can a timezone ever become
>     invalid?  We do
>     have old names, where a timezone has had the name we call it by
>     changed - then
>     we keep the old name forever, for backward compatibility (possibly
>     except for
>     a case where it existed such a short time with the wrong name that
>     it would
>     probably never have been used - but I don't think that case has
>     ever arisen.)
> Probably I'm using the wrong term. Let me try to explain with another 
> example.
> Argentina/San_Juan. IIRC, it has a different timezone than the rest of 
> Argentina for one year or so and then they switched back to the Buenos 
> Aires timezone. So, what I mean by invalid is keep a different name 
> when the differentiation doesn't exist anymore. Even in those cases


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