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From: dmark@acsu.buffalo.edu (David Mark)
Newsgroups: comp.databases,comp.software-eng,comp.infosystems
Subject: Re: Time Zones HELP!
Message-ID: <69280@eerie.acsu.Buffalo.EDU>
Date: 5 Apr 91 23:02:25 GMT
References: <1991Apr5.103756.18982@news.cs.indiana.edu>
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In article <1991Apr5.103756.18982@news.cs.indiana.edu> vogt@iuvax.cs.indiana.edu (Michael Vogt) writes:
>Hi,
>
>I'm hoping you can help us with a design problem we have come across.
>
>What date/time format do people use when dealing with data
>that crosses date and time zones?  How are time changes like daylight
>savings time and standard time dealt with?  
>

It seems that the way email and news handles this would be a good way.  This
seems not completely consistent, however.  Most of the email and news I 
received today has dates and times in GMT (Greenwich Mean Time):

Date: 5 Apr 91 21:08:15 GMT
Date: 5 Apr 91 06:18:40 GMT
Date: 5 Apr 91 10:21:27 GMT
etc.

But one item I got today had a local time/date expressed thusly:

Date: Wed, 3 Apr 91 09:19:03 -0800

(that is Pacific Standard Time).

If the database and the transactions are all in GMT, or in offsets from GMT,
then all you need is a good lookup table for local time, whether daylight
savings time is in effect, etc.

> How do flight/navigation/distribution systems handle different
> date/time zones?

Occasionally, they don't handle it perfectly.  About three years ago, we went
to a conference in Phoenix, Arizona, and the dates straddled the start of
datlight savings time in the USA.  The itinerary from the airline or travel
agent had the time one-hour wrong (and one of us almost missed his flight)
because the system did not "know" that Arizona does NOT go on daylight
savings time!

David Mark
dmark@acsu.buffalo.edu