[tz] Request RE: academic research question re: TZ database

Andrew Lyon lyoncatch at shaw.ca
Thu Jan 9 14:15:07 UTC 2020

Thank-you both Paul and Scott for your insight. 

I will modify my language in the future about calling the tz database a source of truth. 

Our local problem and software crash occurred on Android devices interfaces with a large database system (the SCC Soft Computer 'Softlab' system). It appears that if the hour of birth is unknown (for patients born 1930-41), that a birth hour of midnight is assigned as a default. Midnight to 00:59:59 is the hour moved forward for daylight saving time 1930-41, so a birth hour of midnight does not exist in UT. It is likely that the Android system was running a JavaScript code and we are seeking help from the manufacturer to confirm that in the error logs available to the manufacturer. We may never know all the details, but it is an interesting and somewhat querky observation that could occur in any timezone with a history of using daylight saving time a sometime in the past ~100 years. 

regards, Andrew 

From: "Scott Kilpatrick" <skilpat at gmail.com> 
To: "Paul Eggert" <eggert at cs.ucla.edu> 
Cc: "lyoncatch" <lyoncatch at shaw.ca>, "tz" <tz at iana.org> 
Sent: Thursday, January 9, 2020 7:08:41 AM 
Subject: Re: [tz] Request RE: academic research question re: TZ database 

Hi Andrew, 
Regarding the software problem you're seeing, it's quite possibly a result of using a language or API in which dates -- like 2020-01-09 -- are represented as localized datetimes at midnight -- like 2020-01-09 at 00:00 in America/Regina. This is a pervasive class of bugs that affects JavaScript programs for users in Brazil and Chile in particular. JavaScript because the language's builtin Date representation is a datetime (and the ubiquitous moment library isn't so careful with it), and Brazilian and Chilean users because until recently their time zones had midnight spring forwards. Here's a particularly illuminating example of this class of bugs: [ https://github.com/airbnb/react-dates/issues/776 | https://github.com/airbnb/react-dates/issues/776 ] . 

Hope that helps you track down your software issue. 

Scott Kilpatrick 
[ http://typesandtimes.net/ | https://typesandtimes.net ] 

On Wed, Jan 8, 2020 at 8:07 PM Paul Eggert < [ mailto:eggert at cs.ucla.edu | eggert at cs.ucla.edu ] > wrote: 

On 1/8/20 11:49 AM, Andrew Lyon wrote: 
> It appears that many use the tz database as a source of truth. 

Ouch. As we say in big letters, "The tz code and data are by no means 
authoritative." < [ https://data.iana.org/time-zones/tz-link.html#changes | https://data.iana.org/time-zones/tz-link.html#changes ] > 

> I understand there were 10 years between 1930 and 1941 when the hour of 
> Spring daylight saving transition was 0000 (midnight) to 0100. I would 
> like to confirm these entries are in the tz database. 

Yes, tzdb says the 10 years 1930/1934 and 1937/1941 all did that, as can 
be seen from the extract Brian emailed. 

> I have numerous 
> references that daylight saving time was also observed in 
> America/Regina during world war ONE ( 1914-1918) and I am uncertain if 
> those entries are in the tz database or the hour of those transitions. 

As Brian mentioned, tzdb has these two transitions for 1918: 

Sun Apr 14 08:59:59 1918 UT = Sun Apr 14 01:59:59 1918 MST 
Sun Apr 14 09:00:00 1918 UT = Sun Apr 14 03:00:00 1918 MDT 

Sun Oct 27 07:59:59 1918 UT = Sun Oct 27 01:59:59 1918 MDT 
Sun Oct 27 08:00:00 1918 UT = Sun Oct 27 01:00:00 1918 MST 

However, there's a good chance these data entries are incomplete for 
Regina. It's also possible that the entries for 1930/1941 are wrong. For 
details, please read the commentary for Regina in the northamerica file. 
Here's the current development version: 

[ https://github.com/eggert/tz/blob/master/northamerica | https://github.com/eggert/tz/blob/master/northamerica ] 

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