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Re: [COAS-List] UTC offset? string TimeStamp?
I think you make some excellent points. I'm not sure COAS needs its own
Time definition, either. If you adopt the string format, though, I think it
means you need some other mechanism to handle the wild-carding and open
ended time intervals (such as a logical element) for TimeSpan.
Dave
Larry Hamel writes:
> y'all,
>
> as i study time standards in relation to COAS, i'm coming full-circle back
> to a UTC (GMT) offset rather than a timezone code, and questioning use of a
> COAS-invented struct to represent time.
>
> explanations of the ISO 8601 date/time standard can be found at
>
> http://www.cl.cam.ac.uk/~mgk25/iso-time.html
> http://www.roguewave.com/products/resources/exchange/iso8601.html
> http://www.hut.fi/u/jkorpela/iso8601.html
> http://www.w3.org/TR/NOTE-datetime
> http://www.lanl.gov/projects/ia/stds/ia830210.html
>
> these point out (at bottom are excerpts) that there's no international
> standard for timezones, and if there were, keeping up with international
> legislation about timezones would be quite a challenge for such a standard.
> this reference:
>
> http://www.magnet.ch/serendipity/hermetic/cal_stud/newman.txt
>
> mentions a IANA registry of timezone names, but the iana.com site has no
> information about timezones that i can find. keep in mind that if we
> record a timezone instead of an offset to UTC, and subsequently the
> definition of the timezone/daylight-saving changes, we would need a
> historical table of timezone definitions to recapture the offset information.
>
> furthermore, as i read more about ISO 8601 and see how we're trying to
> accommodate flexibility in a TimeStamp struct, i'm motivated to ask: why
> is COAS inventing a new struct TimeStamp? a string TimeStamp can flex
> quite well when there are unknown parts of a time or date, and it can be
> well-specified with constants
> for minimum
> (const string EARLIEST_TIME = "1582-10-15T00:00:00Z")
> and maximum
> (const string LATEST_TIME = "9999-12-31T23:59:59Z") times.
>
> the ISO 8601 format is human-readable for debugging, and there are existing
> implementation libraries (like java.sql.Timestamp) that provide Calendaring
> and comparison operations for it.
>
> why not use ISO 8601, a formatted string, for the COAS TimeStamp?
>
> larry
>
> ---------------
> 6.1. Problems Too Hard to Solve
>
> Since local timezone rules are set by local governments, the only
> authoratative reference for such rules is those governments, most
> of which do not currently provide their rules on line in a computer
> parsible format. In addition, local timezones were historically
> set by cities and towns, so attempting to exhaustively enumerate
> all historical timezones for use in representing past dates is not
> practical. Attempting to predict where new timezones will be
> created as a subset of the area covered by an old timezone is also
> a hopeless prospect.
>
> -----------------------
> Time Zone
>
> <snip>
>
> There exists no international standard that specifies abbreviations for
> civil time zones like CET, EST, etc. and sometimes the same abbreviation is
> even used for two very different time zones. In addition, politicians enjoy
> modifying the rules for
> civil time zones, especially for daylight saving times, every few years, so
> the only really reliable way of describing a local time zone is to specify
> numerically the difference of local time to UTC. Better use directly UTC as
> your only time zone where this is possible and then you do not have to
> worry about time zones and daylight saving time changes at all.
>
> More Information about Time Zones
>
> Arthur David Olson and others maintain a database of all current and many
> historic time zone changes and daylight saving time algorithms. It is
> available via ftp from elsie.nci.nih.gov in the tzcode* and tzdata* files.
> Most Unix time zone
> handling implementations are based on this package. If you want to join the
> tz mailing list, which is dedicated to discussions about time zones and
> this software, please send a request for subscription to
> tz-request@elsie.nci.nih.gov. You can read previous discussion there in the
> tz archive.