[tz] Pre-1970 data

[Clive D.W. Feather]

Paul Eggert via tz said:
> On 10/18/21 06:07, Stephen Colebourne via tz wrote:
> > What tzdb previously offered was a set of IDs,
> > based on a simple rule - "ID as needed for post-1970 data, with at
> > least one per ISO country".

But there's an even simpler rule: "ID as needed for post-1970 data".

> > Full history was available for each of
> > these (whether accurate or not).
> 
> That wasn't ever the case. For example, there was never full history 
> (accurate or not) for San Marino. We shouldn't base our analysis on the 
> idea that we formerly had at least one Zone per ISO country, as we never 
> had an ironclad rule like that and we did just fine without any such rule.
> There's no *timekeeping* reason to require a Zone for every ISO country. 

I agree with this.

> Adding such a requirement would complicate maintenance. It would add a 
> significant amount of likely-bogus data, as witness the recent 
> discussion about the likely-bogus data for Bamako that's in 'backzone'. 
> And it would increase the role of politics particularly as new countries 
> emerge, and politics is something we should avoid as much as possible.

Suppose that a new "country" (quotes because not all ISO 3166-1 entries are
countries and I *REALLY* don't want to start arguing which ones are) is
formed. We now have to split a zone into two with identical post-1970 data.

But what do we use for the pre-1970 data? One of them will have to take
data for a city in a different country. Precisely what Stephen has been
arguing against!

We need to decide what TZDB's policies are in relation to pre-1970 data,
including when and where the data is included, how to indicate the
reliability of the data, and how to handle zone splits and merges.

> What I am sensing from your proposal, as well as from some of the 
> followup comments, is a need to further clarify exactly what the tzdb 
> project's interfaces are.

I agree with this. I think it should have priority over the rest of this
discussion.

-- 
Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
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