What is a time zone?

David Keegel djk at cyber.com.au
Tue Feb 13 22:58:54 UTC 2001


As a hypothetical question, what would need to be changed in tzcode/tzdata
to make libtz suitable for your application?

The benefit to you of doing this would be that you wouldn't have to keep
updating the DST rule data yourself - it seems like there is always someone
in the world wanting to change their DST rules, so doing this properly is
a lot of work.  Easier to just ftp the latest data every month or two.

Even if you don't want to change your application, it may be instructive
for us to get a better handle on what people want in the real world that
isn't currently in tz, so that the next programmer can use libtz.

] Currently in our application we have two tables,
] 1) DSTRule:-
] RuleName
] StartMonth
] StartWeek (First, Second, Third, Fourth, Last)
] StartDayOfWeek(Sunday)
] StartDate(This column is mutually exclusive from previous 3 colums, to
] support countries where DST starts and ends on specified dates)
] EndMonth
] EndWeek
] EndDayOfWeek
] EndDate
] 2) DSTRuleException (This stores any exception from the rule for a given
] year)
] Year
] StartDate
] EndDate
] Regards,
] -Syed
] -----Original Message-----
] From:	Thomas Carey [mailto:tcarey at bluetrain.com]
] Sent:	Tuesday, February 13, 2001 2:23 PM
] To:	Syed.Sajjath at wcom.com; 'Gwillim Law'; tz at elsie.nci.nih.gov
] Subject:	Re: What is a time zone?
] I am certainly interested in consuming such data :)
] My question is - what does the "DST rule table" required to augment such a
] list look like?
] thanks
] tc
] ----- Original Message -----
] From: "Syed Sajjath" <Syed.Sajjath at wcom.com>
] To: "'Gwillim Law'" <gwil at mindspring.com>; <tz at elsie.nci.nih.gov>
] Sent: Tuesday, February 13, 2001 11:50 AM
] Subject: RE: What is a time zone?
] I work for a conferencing application and our main interest in timezones is
] to convert the scheduled conferencing date to a users local time and an
] operators local time.  There are two entities involved, the operator and the
] conferencing user.  The operator need not be in the same country as the
] user.  For example if the user is from India, the operator is in Hong Kong.
] When the user schedules the call, he mentions that he wants to schedule a
] call at 10:00 am Indian Standard Time.  When the operator gets the
] worksheet, (s)he gets the time converted to Hong Kong time, 12:30 PM HKT.
] The point I would like to make is the user is, the user knows only his
] timezone would be clearer to him if we present IST, India as his timezone
] rather than UTC+ 5:30, and when the operator gets the worksheet (s)he is
] interested in knowing the time in Hong Kong Time.  I know language is a
] barrier, but we do attempt to store what the locals call the timezone, so it
] is easier for scheduling in their time.  How do we know IST is for Indian
] Standard Time?  We always assosciate the abbreviation with a country, so
] when the user is from India IST stands for Indian Standard Time.  Same way
] if an Australian user asks for 10:00 am EST, we know it is australian time,
] not US.  Whether it is Standart or Summer we calculate based on the
] scheduled time(our assumption is user just wants the conference at that
] local time).
] For this reason, assuming others also have similar applications, I had
] requested the tz list to consider having a standardized file with specified
] format (only for timezones effective as of now and updated regularly).  John
] Halloran (I thank him for the prompt reply) had replied with a list, but
] that is not the format I wanted and the list is not complete either.  For
] example as pointed out by Alex, Burma is not in the list.  Also there are
] two rows for US Eastern Daylight Time and Eastern Standard Time.  I would
] like something in the format.
] Country , Zone Short Name, Zone Long Name, Standard Short Name, Standard
] Long Name, Daylight Short Name, Daylight Long Name, GMT Offset, DST Rule
] Name, DST Offset
] United States, ET, Eastern Time, EST, Easter Standard Time, EDT, Eastern
] Daylight Time, -5:00 , United States, 60 mins.
] Is anybody in this maling list interested in such a database or have such an
] application?  If so, I would be interested in discussing how they are using
] the tzdata, and is there anything we can do together to make maintain our
] database in sync with tzdata.  For now I maintain an Oracle database and
] manually update the entries.  I have also written my own APIs to support
] other programmers needing time conversions.
] Regards,
] -Syed

 David Keegel <djk at cyber.com.au>  URL: http://www.cyber.com.au/users/djk/
Cybersource P/L: Unix Systems Administration and TCP/IP network management

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