Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!att!pacbell.com!ames!dftsrv!ukma!seismo!beno.CSS.GOV
From: jean@beno.CSS.GOV (Jean Anderson)
Newsgroups: comp.databases
Subject: RE: Time Zones HELP!
Message-ID: <49534@seismo.CSS.GOV>
Date: 6 Apr 91 21:30:34 GMT
Sender: usenet@seismo.CSS.GOV
Organization: SAIC Geophysics Division, San Diego, California
Lines: 37

In article <1991Apr5.103756.18982@news.cs.indiana.edu> vogt@iuvax.cs.indiana.edu (Michael Vogt) writes:
>
>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?  
>

We work with world wide seismic data.  We store all times in GMT 
"epoch" time--the number of seconds since midnight January 1, 1970
(I suppose immediately tagging this as the UNIX-based system it is).

By default we also display GMT rather than convert to localtime.  That
avoids having to know time change schedules and hour offset.  For example,
the USA goes on Daylight Savings this Sunday, but Norway already switched 
last weekend.  "Let's see here....this data came from Norway so subtract 9
hours to get my PST. Oops--today subtract 10 because they already switched
to Daylight Savings and we haven't yet."   Three months from now it would be 
even worse for somebody looking at old data.  Who ever remembers the exact 
day that each country switches from Standard to Daylight?  Such confusion
could result in significant errors.

Epoch time is stored as a double precision float in the database, but we 
have library routines that convert it to a variety of human readable 
date/time formats.  And for interactive ORACLE users, we have SQL*Plus 
defines specified up in the global startup file (glogin.sql) to likewise 
convert to human readable date/times.

It is much easier to deal in GMT.

+----------------------------------------------------------------------------+
| Jean Anderson, DBA                            email:  jean@seismo.css.gov  |
| SAIC Geophysics Division, Mailstop 12            or:  jean@esosun.css.gov  |
| 10210 Campus Point Drive                      phone:  (619)458-2727        |
| San Diego, CA  92121                            fax:  (619)458-4993        |
+----------------------------------------------------------------------------+
|                Any opinions are mine, not my employer's.                   |
+----------------------------------------------------------------------------+