[tz] [PROPOSED] Merge timezones that are alike since 1970

David Patte dpatte at relativedata.com
Wed Jun 2 00:57:06 UTC 2021

I should add that as an app developer, i do not use zic at all, so I 
have no need for enhancements to zic.

I write both astronomy and family history apps, and I write my own 
parsers to extract the data I  want from tz tables on the fly. I believe 
many using the historical data portion of tz would likely do the same 
thing. Type (2) people simply want to continuously improve the 
accessibility, locality and accuracy of historical tz data, for apps 
that want PAST tzdata, not future tz data.

On 2021-06-01 19:48, Paul Eggert wrote:
> On 5/30/21 8:10 AM, David Patte via tz wrote:
>> 1) On one hand, several people would like to simplify the main data 
>> table, reducing the number of individual zone records by merging them 
>> where they are the same since 1970....
>> 2) On the other hand, several people would like to have tz be a 
>> source, maintain and collect more historical tz data and organize it 
>> by international standards so the historical data can be expanded per 
>> country....
>> So, I have a question. And I'm not trying to difficult.
>> Assuming that the goal of (1) is achieved, what can be done to not 
>> undermine type 2 users? If we have (1), but also want to maintain and 
>> expand historical data per country's zones, how could that be done? 
>> using a secondary table? Could the back table be improved, expanded 
>> and enhanced?
> These are good questions. We have the 'backzone' file for type (2) 
> data, but the 'backzone' approach is apparently unsatisfactory for 
> some users of type (2) data.
> Part of the problem may be that 'backzone' is a mishmash quality-wise. 
> Today there are only two simple options in the Makefile - use either 
> all of 'backzone' or none of it - and there are real problems with 
> using all of it. Perhaps we could add something that would give users 
> more flexibility.
> For example, if a downstream user wants the 'backzone' entry for 
> Europe/Stockholm which is well-documented, but doesn't want backzone's 
> America/Montreal entry because it's not well-attested and is most 
> likely wrong, the user could specify a list of backzone names that 
> includes Europe/Stockholm but excludes America/Montreal. I think it 
> would not be too much work to add something like this to the tzdb 
> code. This would better support users who want a separate Zone for 
> each country in 'backzone', but do not want all of 'backzone'.

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