Subject: RE: RECUR issue: DST-change anomalies

From: "Lowde, Chris A" <[email-masked]>
Date: Thu, 22 Mar 2001 17:17:36 -0600

If you are storing it in local time then you are not using time zones.  If
it is stored in terms of the local time zone how are you differentiating
between CDT and CST.  And if you are using the time zone then there is
explicitly not an issue since 01:30CDT is not the same as 01:30CST

If it is defined in a particular time zone then it can be stored in terms of
GMT and then there is implicitly not an issue.

Of course this raises the whole issue of there are schedules that are
absolute, ie relative to GMT, and that are local, ie 02:00 no matter what
time zone I am in.  Any event needs to be tagged so that it can
differentiate it.  I see so many systems that tag an anniversary date in
terms of the time zone that the entry was entered in, and then you change
time zones and the anniversary date changes, this is not generally a useful
concept.

-----Original Message-----
From: John Stracke [mailto:[email-masked]] 
Sent: Thursday, March 22, 2001 14:46
To: calsch WG
Subject: Re: RECUR issue: DST-change anomalies

"Lowde, Chris A" wrote:

> An event such as this should only fire once,

How do you decide which time?

> And it gets worse if the local system is on a laptop and travels
> between two time zones at 01:45 and resets the system clock.  Now they get
> four hits.

No, it doesn't; the event is defined in a particular timezone, not in "local
time".

Of course, you would have a problem if "resets the system clock" does not
involve specifying a timezone.  Reasonable OSes store their system clock in
GMT, and let each process worry about timezone on its own.

> The user agent can warn the user and have them pick one time.

Yes, it should.  However, the UI is separate from the code that expands the
recurrence; that code needs to do something predictable, since it can't ask
the user what to do.

> Note when the clock moves forward there is an hour that never appears in
> local time

Yes, I did mention that.

--
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|John Stracke    | http://www.ecal.com |My opinions are my own.|
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---

From: John Stracke <[email-masked]>
Date: Thu, 22 Mar 2001 20:47:00 -0600

> explicitly not an issue since 01:30CDT is not the same as 01:30CST

Nobody schedules recurring events in CDT or CST.  You specify it as "Central
Time", and know that the GMT offset will change.  If you were to specify a
weekly event as "0900 CST", then it would start at 9:00 AM in the winter and
8:00 AM in the summer.  The GMT offset would stay the same, but who cares?

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