Time Zone Localizations

Paul Eggert eggert at CS.UCLA.EDU
Mon Jun 14 04:16:36 UTC 2004

"Mark Davis" <mark.davis at jtcsv.com> writes:

> 1. What are the all valid Olson TZIDs
> 2. How to determine which are 'canonical' and which are simply included for
> compatibility
> ...
> 5. An explicit description of the data representation for all of the
> data files.

We've covered these issues in our emails so far, I think, so all you'd
need to do is write it all down.

> 3. What is the meaning of an TZID

Sorry, I don't know what you mean by "meaning of a TZID".
A TZID is just a name.  But perhaps you can just consult
the Theory file to see the naming convention.

> 4. What is the versioning scheme,

You can get many (most?) old versions at
<ftp://munnari.oz.au/pub/oldtz/>; the versioning scheme should
be fairly evident though I suppose it wouldn't hurt to write it up.

> including assurance that:

I'm afraid there is no warranty of any kind.  This is entirely an
informal volunteer effort.

>     - once a version is issued it is never changed.

That's been true in practice.  For example, once tzdata2003d.tar.gz
was issued, it wasn't changed; instead a newer version
tzdata2003e.tar.gz was issued.

> - TZIDs are stable, in the sense that they will never be withdrawn or reused
> with a substantially different semantic in later versions

That's also been true in practice, mostly.  Generally speaking, TZIDs
are never withdrawn; they're just moved to the 'backward' file.

However, I can think of one exception.  In 1994 some of the
GMT-related TZIDs did change their semantics to conform to POSIX.  For
example, the old TZID "GMT-12" was withdrawn and its replacement is
called "Etc/GMT+12"; this because POSIX required a different semantics
for TZ="GMT-12".  This sort of confusion is one of the reasons why I
don't encourage the use of TZIDs like "Etc/GMT+12".

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