Timezones (was: limits of the generic)
Jeni Tennison scripsit: > Of course when you schedule something down to the particular day, then > you can *know* what timezone is relevant. So I can tell my friend "my > plane touches down at 2002-11-29T09:45:00-05:00 > (2002-11-29T14:45:00Z)" (I'll assume we're both geeks, so she > understands ISO 8601-formatted date/times). Actually, you can't *know* it. Washington or Albany might decide to change the timezone rules between now and then, in which case the UTC time would change. Historically, the safest thing is to label the zone "America/New_York", which reflects a certain historical pattern of timezone use. This is not the same as "America/Montreal", because that has a different pattern of zone switches, and furthermore is under the control of a different national authority that could cause it to migrate away from America/New_York, as was the case in 1974-75. Only past or present events can safely be labeled by a mere offset from UTC time. Future events, unless they are *scheduled* in UTC time (like astronomical events), need more information. The entirely non-standard and unofficial (but generally used on all non-Windows platforms) ADO timezone system recognizes about 400 distinct zones worldwide, labeled by continent and largest city. -- Not to perambulate || John Cowan <jcowan@r...> the corridors || http://www.reutershealth.com during the hours of repose || http://www.ccil.org/~cowan in the boots of ascension. \\ Sign in Austrian ski-resort hotel
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