[tz] Fwd: TZDB Questions

Paul Eggert eggert at cs.ucla.edu
Tue Aug 28 06:21:42 UTC 2018

> From: Mikey Schott
>     1. Has there been any consideration to move the source data into a more
>     structured format like csv, xml, or json?

There are translators into various XML and JSON flavors; see 
<https://data.iana.org/time-zones/theory.html> for a few pointers. This is the 
first I've heard CSV suggested.

Part of the fun of maintaining tzdb is that the source data format is simple and 
easily readable. I have my doubts whether hand-maintaining the source in these 
other formats would be worth the trouble.

>     2. The latest zone entry for some zones that no longer use dst still
>     point to dst rules, e.g. Asia/Tokyo and the Japan rule set even though dst
>     is no longer used in Japan . Is there a reason why some non-dst zones use
>     this method where they point to an outdated rule set whereas most non-dst
>     zones use no rule set (i.e. rule = '-')?

To some extent it's an accident. To some extent it attempts to use a ruleset 
that is likely to see the smallest change if the most-likely political events 
occur in the future. I don't try all that hard to normalize the source; the goal 
is easy of understanding and stability more than strict consistency.

>     3. I've noticed that some zones just use a shortened version of their
>     offset for their format, whereas timeanddate.com gives them a more
>     descriptive format (e.g. Europe/Volgograd uses MSK vs. +03). Is there a
>     reason for the discrepancy? Does the time zone database error on the side
>     of caution here?

Yes. Previously we erred on the side of incaution and saw more arguments over 
what the abbreviations should be. The abbreviations were kind of fanciful, and 
not that useful anyway (they're ambiguous). This is described in more detail in 

>     4. I believe that one of the primary purposes of the Link zones is to
>     ensure that there is a zone that covers every country.

That has been the case, yes. In hindsight this was a mistake as it needlessly 
complicates tzdb and is more likely to lead to political bickering.

>     Is there a specific
>     list or source that the time zone database uses to decide the list of
>     countries that are covered?

More politics?! The list we use is in the file iso3166.tab. It is not 
authoritative nor, as the lawyers might say, is it intended to take or endorse 
any position on legal or territorial claims.

>     5. Do you have a favorite time zone?

My current favorite is America/Montevideo. "Apparently restaurateurs complained 
that DST caused people to go to the beach instead of out to dinner." Imagine, a 
government that listens to its country's cooks!

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