[tz] Rules for TZ+ database

Guy Harris guy at alum.mit.edu
Thu Sep 5 18:28:53 UTC 2013

On Sep 5, 2013, at 7:57 AM, Lester Caine <lester at lsces.co.uk> wrote:

> Paul Eggert wrote:
>>> most end consumers of the data cannot tell the
>>> >difference between a Link and a Zone. As such, from their perspective
>>> >it is very odd to find that some IDs are allowed pre-1970 data and
>>> >others are not
>> If we're talking about the perspective of most end consumers,
>> most of them don't know or care about pre-1970 data.
>> So they won't find anything odd at all.
> The problem with that statement is that 'some' end consumers do. Any application which displays historic data via a timeline ( how far does facebook go back? )

...and do items in the timeline have time stamps for entries created before Facebook existed or do they just have dates?  If they just have dates, then Facebook, at least, won't care.  If they have times, are they represented as something such as a UTC-based seconds-{before,since}-the-Epoch or are they represented as local time (so that if the user starts their timeline with "Born on March 4, 1957, at 4:27 PM", that's how it's reported to all Facebook users, regardless of what time zone they're in).

I think it's non-negotiable that there will be packagers of the tzdb who will winnow out information that requires having different zones for regions that differ only in pre-1970 behavior, and that we will provide a mechanism for them to do so; some consumers do care about pre-1970 data, but if they're running on an OS that winnows out pre-1970 differences, they may have to use their own un-winnowed version of the tzdb.

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