[tz] Adding verified historic details

[Russ Allbery]

Lester Caine <lester at lsces.co.uk> writes:
> Russ Allbery wrote:

>> This sounds like a good idea to me, although I don't know what
>> difficulties it poses for the rest of the software.  It would indeed be
>> nice to not have to duplicate all the rules into a separate zone when
>> the zones are identical after a certain date, and it also seems like it
>> would make some possible winnowing strategies more straightforward.

> Fix the current holes in the system so that we can handle all the missing
> data before writing software to take it way again?

It sounds like you may have misunderstood the intent of winnowing.

Winnowing provides a mechanism to generate selected subsets of the raw
database so that, for example, user time zone selection is not confused by
multiple time zones that, from the perspective of the average user, have
no interesting differences.  It doesn't take any data away; the raw data
is still present.  It just provides ways of generating reduced views on
that data.

The specific concern here as I understand it, and the concern I would have
when looking to deploy software based on the tz database, is that the
addition of more correct pre-1970 data will, if done properly, result in
an explosion of new zones that are not of interest to the vast majority of
users of the tz database.  Given that, we should provide some mechanism to
present them with the collapsed post-1970 view (at least) prior to
creating that explosion of new zones so that they can choose the level of
granularity at which they want to operate.

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