[tz] Rules for TZ+ database

Stephen Colebourne scolebourne at joda.org
Fri Sep 6 09:39:24 UTC 2013

On 5 September 2013 15:08, Stephen Colebourne <scolebourne at joda.org> wrote:
> On 5 September 2013 13:55, Paul Eggert <eggert at cs.ucla.edu> wrote:
> Its important not to forget the existence of non zic parsers here.
> Adding lots of new data to the current set of files would impact them,
> forcing them to use all the new IDs or implement their own winnowing.
> Whereas if the additional zones were placed in a new file "extended",
> then zic and non-zic consumers could easily choose whether to include
> the extra data or not.
> None of the above should stop existing Zone and Link entries from
> being expanded with researched historic data. ie. pre-1970 data for
> the existing set of IDs should remain in the main files, unless an
> entirely new data format is being created (which I'm not enthused
> about).

Just to outline my needs from the dataset:
- the full time-zone history for all IDs currently in the "main" files
- the old IDs located in the "backward" file

The current way of working appears to be is:
- the full time-zone history for all Zones currently in the "main" files
- no time-zone history for Links currently in the "main" files
- the old IDs located in the "backward" file

Note that the only IDs I need are those IDs that are currently deemed
important enough to be in the current tzdb. I don't need any more IDs,
or any more accurate history for locations (such as the difference
between Paris and Lyon). I do need full history, if available, for IDs
currently defined as Link entries.

The discussion is proposing a variety of extensions and file format
changes, but to actually achieve the minimal extension outlined above
will require parsing and understanding the full set of extended data.

My preferred solution would be to allow Link entries to be converted
to Zone entries if and when the history becomes available. With a
winnowing solution, this would have no impact on data sizes or
performance AFAICT.

Summary, there is a middle ground between not caring about pre-1970
and caring about everything. I don't want the need for that middle
ground to be lost.


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