From twinsun!twinsun.com!eggert@CS.UCLA.EDU Tue Oct 19 15:08:13 1993 Return-Path: <twinsun!twinsun.com!eggert@CS.UCLA.EDU> ... From: eggert@twinsun.com (Paul Eggert) Message-Id: <9310191858.AA24533@spot.twinsun.com> Date: 19 Oct 1993 11:58:24 -0700 To: ado@elsie.nci.nih.gov Subject: Shanks's International Atlas ...

In looking through Shanks's atlas I see a number of points that perhaps need further thinking before I sit down and try to generate more tables. The main point is that we need to decide what the limitations of the tz database should be. I'd appreciate your advice on the following points, which are roughly in decreasing order of seriousness.

There are many, many tables. E.g. France has 153 tables; most of the variants occurred during World War II, as the fortunes of war caused different districts to switch between French and German time zone rules. Do we really want a directory labeled `France' with 153 files in it, one per district? Even coming up with the district names will be a chore, as Shanks merely gives each table a number and, for each city, tells you which time table it uses.

Even the number of countries would mean that the timezone database would be very bushy at top level, with entries ranging from Afghanistan to Zimbabwe. Perhaps some substructure is in order. At some point you mentioned using ISO country codes? (But how many people know their country code?)

The current code makes no provision for when a district changed from LMT to standard time (e.g. 1914 Jan 1 in Albania). Strictly speaking, it's incorrect to give times other than LMT before the switch. At least we should put in a comment when LMT began, I suppose. But should there be some provision in the code as well? I suppose it would be something like a suffix to the TZ value which specifies the LMT offset when LMT is in effect, since you can't possibly have a table for each LMT offset.

I doubt whether the following points are worth worrying about in the code, but perhaps there should be a commenting convention for documenting these points.

Some countries switched from the Gregorian to the Julian calendar in this century; e.g. part of Bulgaria held out until 1920 Sept 17 (Gregorian). I suppose this is too much for the TZ code to handle, but perhaps comments are in order.

The Soviet Union instituted a 5 day week in 1929, a 6 day week in 1932, and reverted to a 7 day week in 1940.

China changed from the Chinese calendar on 1912 Feb 12 (Gregorian); Japan from the Japanese calendar on 1893 Jan 1 (Gregorian).

There was a time before LMT, when people used apparent time, not mean time. E.g. Paris switched from apparent time to LMT in 1816.