[tz] Recommendations for stable list of timezone ids

[Mark Davis ☕️]

In CLDR we have had to produce a stable set of TZIDs as well, so you might
look at that. (We also have to have short IDs, so we developed those based
where possible on UNLOC codes.)

Mark

On Fri, Feb 9, 2018 at 1:44 PM, Tobias Lindaaker <thobes at gmail.com> wrote:

> I am trying to compile a flat list of all tzids in the Time Zone Database
> in a way such that the position of a tzid remains the same in the list even
> in the face of future changes to the Time Zone Database.
>
> I would like to know if anyone could provide me with some insight into how
> (a prefix of) such a list could be generated from any version of the Time
> Zone Database. Or would this be something I would have to maintain myself
> from release to release of the Time Zone Database?
>
> The requirements I would have for generating this list would be that given
> two releases of the Time Zone Database, X and Y. If X is released before Y,
> then the list generated from X must be a prefix of the list generated from
> Y (and vice versa: if Y is released before X, the list generated from Y
> must be a prefix of the list generated from X).
>
> A simple alphabetical ordering is obviously not going to work, since for
> example the addition of America/Punta_Arenas in 2017a would end up before
> many of the tzids that existed in versions prior.
>
> Since I don't require this to work for all historical releases, my first
> thought was to start from a fairly recent release (tzdata2013h) and verify
> that I got the same order when sorting the timezones based on their
> earliest rule. However the removal of tzids (such as
> Canada/East-Saskatchewan in tzdata2017c) made this impossible, since any
> removal makes it impossible to ensure that prior versions are strict
> prefixes.
>
> It now seems as if I would have to maintain this list myself, tracking
> each release of the Time Zone Database and ensure that any tzids added to
> the Time Zone Database are appended to my list in release order. If
> possible I would very much prefer to avoid this, since it requires me to
> release updates of my software to track the releases of the Time Zone
> Database, I would much rather like it if my software could rely on the Time
> Zone Database available from the system where it was running.
>
> Finally some background on why (I think) I need to generate this type of
> list of tzids: I am improving the support for storing timestamp values in a
> database management system (Neo4j), and would like to avoid having to store
> the timezone component of zoned timestamps as a (variable length) text
> component, but rather store it as a fixed size integer offset into a table
> of tzids. Thus I need such a stable list of tzids.
>
> I have tried searching the archives of this mailing list for similar
> questions before posting, but have not been able to find such an entry. The
> closest I found were a few questions on how to translate the tzids to
> localized names. Since I did not read through the entire archives, but only
> did a search, I apologise in advance if this has been asked and solved
> before, and hope that you will be able to direct my attention to that
> thread.
>
> Thank you,
> Tobias
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