[tz] [PROPOSED] Merge timezones that are alike since 1970

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Wed Jun 2 17:10:34 UTC 2021

On 2021-06-01 20:42, Guy Harris via tz wrote:
> On Jun 1, 2021, at 5:57 PM, David Patte via tz <tz at iana.org> wrote:
>> I write both astronomy and family history apps, and I write my own 
>> parsers to extract the data I  want from tz tables on the fly. I
>> believe many using the historical data portion of tz would likely
>> do the same thing. Type (2) people simply want to continuously
>> improve the accessibility, locality and accuracy of historical tz
>> data, for apps that want PAST tzdata, not future tz data.
> It's not a difference between wanting past data vs. wanting future data.
> OSes definitely use past tz data:
>	$ ls -lT /usr/local/bin/yacc
>	-rwxr-xr-x 1 root wheel 123916 May 6 14:18:05 2018 /usr/local/bin/yacc
> The difference is how far back in time is useful, not whether the
> past is useful at all.
> For OS purposes, times before the OS's time stamp epoch are probably 
> of less interest than times at or after the epoch, and for many
> OSes, even times after the epoch but before the first release of the
> first OS to use any file system supported by the OS are of less
> interest.
> The UNIX epoch is probably a good dividing line between the two groups.

It can be useful to tag (touch) (scans of) historical or official 
documents, pictures, media with real timestamps corresponding to the 
date issued, taken, or expired, as well as location, and time zone info. 
The current range covered by GNU date:

@-67768040609740800  -2147481748 Jan 01 Mon 00:00:00
  @67767976233532799   2147483647 Dec 31 Tue 23:59:59

is stupendously more than historical, supported on BtrFS, BSD UFS2; the 
MS Windows NTFS date range from 1601-01-01 (to 60056-05-28) is more 
useful than the Linux ext2-4 range from 1901-12-13 (to ext4 2446-05-10), 
and Apple FS from 1970-01-01.
J/MPEG EXIF/IPTC/XMP metadata (exiftool) uses ISO-8601 strings, allowing 
for uncertain values specified as 00 or spaces
<https://exiftool.org/forum/index.php?topic=5007.0;all> but not all file 
content formats support user specified metadata.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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