Subject: [Ietf-calsify] DST discontinuities part 3: discontinuities for event end times

From: lennox at cs.columbia.edu (Jonathan Lennox)
Date: Mon Nov 6 16:25:12 2006

My third issue has to do with how you handle the case when an event's end
time "would" occur within a DST discontinuity.

It's hard to even define this issue without a resolution to Issue 27 -- what
DTEND/DURATION mean for events that cross a DST transition.

It sounded like the consensus in the room was leaning towards the idea that
durations are "nominal" durations, not "real" durations, i.e. in
America/New_York, a PT8H event that starts at 2006-04-02 00:00:00, or
2006-10-29 00:00:00, ends at 08:00:00 in both cases (for a real duration of
seven hours or nine hours, respectively).

If that is indeed the case, the question needs to be answered: when does the
event

   DTSTART;TZID=America/New_York:20060402T000000
   DURATION:PT2H30M

end?  The nominal duration would imply an end at 2006-04-02 02:30:00, which
in America/New_York doesn't exist.

Similarly, the nominal-duration rules would indicate that

   DTSTART;TZID=America/New_York:20061029T000000
   DURATION:PT1H30M

would end at 2006-10-29 01:30:00, which could refer to either 2006-10-29
01:30:00 EDT or 2006-10-29 01:30:00 EST.

To be clear, the fact that my examples used sub-day duration lengths isn't
relevant here; the problem also occurs with 

   DTSTART;TZID=America/New_York:20060401T023000
   DURATION:P1D

   DTSTART;TZID=America/New_York:20061028T013000
   DURATION:P1D

as well.  My inclination would be to say that the resolution should be the
same for these both cases, but others may disagree.

This issue is the same both for single events and for recurring events, i.e.

   DTSTART;TZID=America/New_York:20060331T023000
   DURATION:P1D
   RRULE:FREQ=DAILY;COUNT=2

   DTSTART;TZID=America/New_York:20061027T013000
   DURATION:P1D
   RRULE:FREQ=DAILY;COUNT=2

have this problem for their second occurrence.

-- 
Jonathan Lennox
[email-masked]