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1433Re: Dates with timezone information

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  • mattias_flodin
    Jan 14, 2006
      --- In ISO8601@yahoogroups.com, NGUYEN Ivy <nguyenivy@g...> wrote:
      > I think you just indicate whatever default time you use (like 00:00),
      > then use a timezone afterwards. I don't believe dates alone have
      > timezone information in ISO 8601. It wouldn't make sense, unless some
      > new provision is added like 'all dates without times that have
      > timezone information, are to be treated as 00:00 if no time is
      > stated'.
      > It is true that giving a date without a timezone can cause ambiguity,
      > as at least half the world is always a different date than stated. But
      > on the flip-side, if no time within the date is stated at all, than
      > how can we have timezone information? '2000-01-01 in New York
      > (UTC-05)' means that 24-hour period lasting from 00:00--24:00 in New
      > York (timezone). Doesn't reveal much more.

      I don't understand this last comment. Obviously, any date and time you
      specify is a range, if you want to view it that way. If, as you say,
      we can view "2000-01-01" is the range [2000-01-01 T00:00, 2000-01-01
      T24:00), then the time "2001-01-01 T20" could also be seen as the
      range [2001-01-01 T20:00, 2001-01-01 T21:00).

      Any time we represent will be specified to some amount of precision.
      Just providing the date is one level of precision. Specifying the hour
      is a higher level of precision, and indicating minute and second give
      even higher precision. Since the ISO standard doesn't say whether to
      interpret a date as a time range or as a singular point in time, that
      is up to the application as far as I am concerned. Why then should you
      draw a line at which precision level time zones are used?

      If I choose to view a date as a singular point in time (much as many
      would view T20:01:02 as a singular point), then that moment will occur
      at a different local time in different time zones. Obviously we could
      specify at which second it occurs, as in "The Swedish new year occurs
      on 2006-01-01 00:00:00+01:00 and the Chinese new year occurs on
      2006-01-29 00:00:00+08:00", but it is much more convenient to say "The
      Swedish new year occurs on 2006-01-01+01 and the Chinese new year
      occurs on 2006-01-29+08".

      Perhaps the issue at hand here boils down to what is the purpose of
      introducing reduced precision into the ISO standard in the first place.

      Mattias Flodin
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