[tz] Rules for TZ+ database

[Russ Allbery]

Guy Harris <guy at alum.mit.edu> writes:

> By either

> 	1) using your own un-winnowed version of the tzdb

> or

> 	2) only using systems where the vendor guarantees that they're
> 	offering an un-winnowed version of the tzdb, if there are any such
> 	systems.

An obvious approach for distribution packagers would be to provide two
packages that both Provide tzdata, one with the traditionally winnowed
data (1970 cutoff) and one with the full data, and let people pick.  The
one winnowed to 1970 would probably be the one installed by default,
unless the number of additional zones in the unwinnowed version turned out
to not be significant.

I suspect that initial installs would provide only the winnowed data for
initial time zone selection, since that's where a multitude of choices
poses the largest UI concern.

One very interesting thing that this proposal offers, which is not
currently available, would be to build a custom set of tzdata for the
install process that's better-suited to the UI needs of initial
installation and time zone selection.  For example, for installs, I could
see deciding to include only zones whose differences matter for current
time (a cutoff of 2013), but including the data set that ensures that
every ISO 3166-1 code has at least one zone because the geopolitical
issues are particularly acute during the install process.  (Of course, one
would have to be careful that one didn't drop the selected zone if one
switched to a database with a different winnowing property, or provide
some mapping mechanism.)

-- 
Russ Allbery (rra at stanford.edu)             <http://www.eyrie.org/~eagle/>