[tz] Version in zoneinfo files?

Tony Finch dot at dotat.at
Thu Oct 29 13:07:36 UTC 2015

Lester Caine <lester at lsces.co.uk> wrote:
> On 28/10/15 23:37, John Hawkinson wrote:
> >
> > The time and the zone must be stored, becuse whther the time shifts
> > with DST is a function of the zone. As long as the calendar app
> > stores some things like "9:00am US/Eastern" (for a dentist appointment)
> > and "13:00 UTC" (for an international conference call), calendar
> > apps should work well.
> SIMPLE things like that are not the problem. Where the problem arises is
> when the 9:00AM UTC Meeting in one location is advertised in several
> time zones and one of those time zones has a change of offset. The
> medical conference I quoted was across four time zones in Europe and the
> middle east, but one of the satellite links started an hour before the
> delegates arrived because of the change in DST at short notice. Don't
> ask why nobody even thought about the problem ... the local programs had
> been printed only with local times and the local organisers simply did
> not think ... current calendars do not do multi timezone well?


There is a problem with the way iCalendar is often used: calendar apps do
early binding to timezone rules - not just the tz names, but embedding the
actual schedule of DST changes in the calendar appointment object. This is
a massive pain if the rules change.

The best way to avoid problems is to bind to a time zone as late as
possible. Sadly iCalendar doesn't allow the binding to be late enough.

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
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