On 2014-02-16 01:28 AM, John Hawkinson wrote:
This is not a real conflict.
The standards you cite do not say "standard time,"
they say things like "standard time scale" which is parsed as
(STANDARD (TIME SCALE)) not ((STANDARD TIME) SCALE).
etc.
Ah, they are defining "standard time", "standard time of day", and
"clock time".
The note on ISO 8601, 2.1.14 "standard time" says "NOTE This time shift
may be varied in the course of a year."
The note on IEC 60050-111, 111-16-16 "standard time" (that ISO 8601
references) says "NOTE Examples are Central European Time (CET), Central
European Summer Time (CEST), Pacific Standard Time (PST), Japanese
Standard Time (JST), etc."
That includes *both* CET and CEST.
The note on ISO 8601, 2.1.15 "standard time of day" says "NOTE Standard
time of day is called "clock time" in IEC 60050-111."
And IEC 60050-111, 111-16-17 "clock time" describes time as indicated
for "local standard time"
It seems pretty clear they mean "standard time" may include "summer
time". That really *is* in conflict with common use, isn't it?
This comes up in context of attempting to write a definition of
"standard time" as understood in common use (and POSIX, and such). You'd
like to reach to ISO 8601 for the definition, and there you discover
this conflict.
ISO 8601 is an important standard. Besides its famous description of
"representation" is also defines what its representing (Basic concepts,
Time Units, Gregorian calendar).
But it is silent on "daylight savings". It describes representation of
"Local time and the difference from UTC", and "local time" is defined in
2.1.16 - local time - locally applicable time of day such as standard
time of day, or a non-UTC based time of day
It can't, or doesn't, distinguish between New York "standard time"
12:00:00-05:00 and New York "daylight time" 12:00:00-04:00.
"Standard time" in 8601 really is in conflict with common use, I think.
-Brooks
Not optimal but so little in life is.
--jh...@mit.edu
John Hawkinson
+1 617 797 0250
Brooks Harris <bro...@edlmax.com> wrote on Sun, 16 Feb 2014
at 01:23:23 -0800 in <5300838b.8030...@edlmax.com>:
Date: Sun, 16 Feb 2014 01:23:23 -0800
From: Brooks Harris <bro...@edlmax.com>
To: Leap Second Discussion List <leapsecs@leapsecond.com>
Subject: [LEAPSECS] Definition of Standard time - Brooks Harris
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It seems the meaning of the term "Standard time" in common-use and
in POSIX is in conflict with the definitions in ISO 8601 and IEC
60050-111.
Wikipedia (not always an authoritative source)
Standard time
http://en.wikipedia.org/wiki/Standard_time
states:
"Where daylight saving time is used, the term standard time
typically refers to the time without the offset for daylight saving
time.".
That is consistent with my understanding of "Standard time".
POSIX doesn't seem to explicitly state this, but the logic of the TZ
environment and functions are consistent with this definition.
But ISO 8601 and IEC 60050-111 say "standard time" may include time
shifts for "winter time" and "summer time":
In ISO 8601 ----------------
2.1.14
standard time
time scale derived from coordinated universal time, UTC, by a time
shift established in a given location by the
competent authority
[IEC 60050-111]
NOTE This time shift may be varied in the course of a year.
2.1.15
standard time of day
quantitative expression marking an instant within a calendar day by
the duration elapsed after midnight in the
local standard time
[IEC 60050-111]
NOTE Standard time of day is called ?clock time? in IEC 60050-111.
In IEC 60050-111 ---------------
111-16-16
standard time
time scale derived from coordinated universal time, UTC, by a time
shift established in a
given location by the competent authority
NOTE Examples are Central European Time (CET), Central European
Summer Time (CEST), Pacific
Standard Time (PST), Japanese Standard Time (JST), etc.
111-16-17
clock time
quantitative expression marking an instant within a calendar day by
the duration elapsed after
midnight in the local standard time
NOTE Usually, clock time is represented by the number of hours
elapsed after midnight, the number
of minutes elapsed after the last full hour, and, if necessary, the
number of seconds elapsed after the
last full minute, possibly with decimal parts of a second. Examples
of the standardized representation
(see ISO 8601) are 09:01; 09:01:12; 09:01:12,23.
-----------
Is my interpretation correct? Can anyone shed light on how and why
ISO 8601 and IEC 60050-111 are in conflict with common use and POSIX
and how this may have come about?
-Brooks
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