FW: Time Zone Data File Conventions

Paul Eggert eggert at twinsun.com
Fri Oct 17 08:31:54 UTC 1997

   From: 	Wally.Wedel at Sun.COM
   Sent: 	Wednesday, October 15, 1997 4:52 PM

   a) Does "wall clock" mean simply take the time as given applying no

Yes; it means local time.  E.g. in:

Rule	US	1967	max	-	Oct	lastSun	2:00	0	S

the `2:00' means the transition occurs at 02:00 local time.

   b) Does "standard" mean apply DST time shift to given time to find true

Yes.  E.g. in:

Rule	GB-Eire	1972	1980	-	Oct	Sun>=23	2:00s	0	GMT

the `2:00s' means 02:00 local standard time.  At those times there
happens to be a 1-hour DST shift, so this happens to be equivalent to
03:00 local (daylight) time.

   c) Does "GMT" mean apply GMT offset to given time to get true time?

Yes.  E.g. in:

Rule	EU	1996	max	-	Oct	lastSun	 1:00u	0	-

the `1:00u' means 01:00 UTC.  E.g. for Europe/Helsinki, the change
occurs at 04:00 local time, since they are 3 hours ahead of UTC in the

   2) Is the convention for rule naming that when searching for the
   applicable rule, one looks for a rule with the specified name
   covering the specified date? I assume that failure to find a rule
   implies no time shift.

This sounds correct, but to make sure, perhaps you could clarify your
question with an example.

   3) The comments in the data files contain quite important
   information about the actual coded information. Have you considered
   converting them to HTML to get them better tagged? I'm particularly
   interested in tagging some kind of a long name usable in reports
   and like.

It'd be nice to have something like that.  Have you looked at zone.tab
and iso3166.tab, and how tzselect.ksh uses these auxiliary tables?
Perhaps this could give you an idea about how to add info and/or
generate HTML.

More information about the tz mailing list