Question on abbreviations
Paul Schauble
Paul.Schauble at ticketmaster.com
Wed Sep 27 22:46:32 UTC 2006
So in this case:
Rule US 1942 only - Feb 9 2:00 1:00 W # War
Rule US 1945 only - Aug 14 23:00u 1:00 P #
Peace
Why is %s undefined in 1943? This was the question that started the
thread. If the time setting carries forward, surely the letter should
also.
++PLS
-----Original Message-----
From: tz-request at elsie.nci.nih.gov [mailto:tz-request at elsie.nci.nih.gov]
On Behalf Of Ken Pizzini
Sent: Wednesday, September 27, 2006 3:14 PM
To: tz at lecserver.nci.nih.gov
Subject: Re: Question on abbreviations
On Wed, Sep 27, 2006 at 02:37:58PM -0700, Mark Davis wrote:
> I share your confusion. If Paul (Eggert's) description is right, then
I have
> to ignore the TO field in some circumstances which are entirely
unclear to
> me. I would much rather see the TO field corrected. That is, if
TO=1942 is
> ignored, and 1945 is the real date, then the line should be corrected
to
> TO=1945.
The key to understanding is that the rules describe a list of
*transitions*.
After a transition, the described effect on zone offset and abbreviation
*remain* in effect until the next transition. The "TO" part of a rule
is
used to enable a shorthand for a _recurring_ transition, such as "first
Tuesday of February", for all years within the range. If "to" is
"only", then the *transition* being documented is a singleton, but
the transitioned-into offset/abbreviation remains in effect until the
_next_ transition, no matter how far in the future.
> There are other failures in the parsing. My error messages are:
...
> I looked into why this is happening, and found:
>
> Zone Europe/Amsterdam 0:19:32 - LMT 1835
> 0:19:32 Neth %s 1937 Jul 1
> But the first LETTER/S defined by Neth is in 1916, so during the range
from
> 1835 to 1916 this is undefined. If the LETTER/S are magically also
defined
> *before* the first FROM, that should be described in the
specification.
Yes, this is a failure of the documentation. If a Zone refers to a time
within a Rule that is before the first transition mentioned for that
rule,
then the _oldest_standard_time_ "Letter/s" is used. In this case, AMT.
> BTW, the documentation was a first a bit confusing to me, since it
says that
> fields are delimited by spaces, and lists a single Zone UNTIL field.
> However, if you look carefully at the documentation, there are really
4
> fields:
>
> UNTIL_YEAR UNTIL_IN UNTIL_ON UNTIL_AT
>
> which are optional [but only in "truncation" from the end: that is, it
> corresponds to the (Perl) regex (UNTIL_YEAR (UNTIL_IN (UNTIL_ON
> (UNTIL_AT)?)?)?)?].
>
> I'm not the only one to have initially made this mistake: the proposed
XML
> format for the TZ database makes the same mistake.
Confusing: granted. Whether "Until" is one or multiple fields is a
matter of interpretation. The _traditional_ understanding is that it
is a *single* "timestamp field" which may happen to have spaces within
it. BTW the subfields aren't "YEAR IN ON AT", but "YEAR MONTH DAY
TIME".
In this regard, a recent addition to the tzcode tarball is
zoneinfo2tdf.pl,
which translates the more free-with-spaces zone tzdata into a form which
strictly uses a single tab between fields. This may make life easier
for some by simplifying their parser's requirements. (Or not.)
--Ken Pizzini
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