[Ietf-calsify] 2nd and higher instance busted across time zone changes.

Jonathan Lennox lennox at cs.columbia.edu
Sun Apr 10 19:56:46 PDT 2005

On Sunday, April 10 2005, "Sam Roberts" wrote to "ietf-calsify at osafoundation.org" saying:

> We need to specify how the subtraction is done when DTEND and DTSTART
> straddle a time shift, and warn implementors to consider the issue I
> think that the DURATION should be in *absolute* time. I.e., 10AM - 5AM
> is 5 hours only if there really are 5 hours between them, and not 4 or 6
> hours (for example).
> I'm not suggesting this as some kind of a normative requirement, just
> that it is easy to calculate offsets with absolute durations if you can
> convert between localtime and UTC - and if you can't do that you'll be
> in trouble.

I think this *should* be a normative requirement; it's clearly the only
meaningful semantic for date-times with time zone references.

Now, how this should be interpreted for floating date-times is another

There's also the question of "does 1 day equal 24 hours", which was the
subject of a long thread on the ietf-calendar list (I think).  Which is to
say, when does an event with DTSTART;TZID=America/New_York:20050403T000000
and DURATION:P1D end?  (Note to non-US readers: Sunday April 3 2005 was this
year's leap-forward date; 24 hours after 2005-04-03 00:00:00 EST is
2005-04-04 01:00:00 EDT.)

Jonathan Lennox
lennox at cs dot columbia dot edu

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