Subject: Re: Last Call: Date and Time on the Internet: Timestamps to Proposed Standard

From: "John Stracke" <[email-masked]>
Date: Fri, 9 Nov 2001 18:10:50 -0500

Keith Moore wrote:

>However, many events are actually specified relative to a particular 
>timezone, and timezone offsets occasionally change with little advance
>warning.  As such, this representation may not be sufficient for 
>specifying dates and times of some kinds of events, particularly
>future events.

This is correct.  The IMPP group covered this in Minneapolis, I think. The 
draft alludes to the problem, but may not be explicit enough (probably 
isn't, if Keith felt it necessary to comment):

   o  All times expressed have a stated relationship (offset) to
      Coordinated Universal Time (UTC).  (This is distinct from some
      usage in scheduling applications where a local time and location
      may be known, but the actual relationship to UTC may be dependent
      on the unknown or unknowable actions of politicians or
      administrators.  The UTC time corresponding to 17:00 on 23rd March
      2005 in New York may depend on administrative decisions about
      daylight savings time.  This specification steers well clear of
      such considerations.)

I believe that Keith is right, that this paragraph should include a 
reference to iCalendar (RFC-2445) and point readers to that for use when a 
simple timestamp won't do.  It's a small point, but it could prevent some 
confusion.

/========================================================\
|John Stracke                    |Principal Engineer     |
[email-masked]   |Incentive Systems, Inc.|
|http://www.incentivesystems.com |My opinions are my own.|
|========================================================|
|"Time is money, and price is information." --Russ Nelson|
\========================================================/

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From: [email-masked]
Date: Sat, 10 Nov 2001 11:13:51 -0500

John, where is the original of this note?  Did it go to the calendar list?
If it's on another list, can you point me to it so I (and the list) can
see the text of the whole note.  Thanks.

"John Stracke" <[email-masked]>
Sent by: [email-masked]
11/09/01 18:10

        To:     [email-masked]
        cc:     [email-masked], [email-masked], [email-masked]
        Subject:        Re: Last Call: Date and Time on the Internet: Timestamps to Proposed
Standard

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From: Donald Craig <[email-masked]>
Date: Sun, 11 Nov 2001 22:00:16 -0800

The use of a UTC timestamp is promoted on the grounds
that a "local" time alternative may have a relationship to
UTC that is "dependent on the unknown or unknowable
actions of politicians or administrators."

However, the relationship between UTC and TAI
(monotonically evenly increasing Atomic Time) is
dependent on measurements collected by the
International Earth Rotation Service (IERS), which
result in the application of leap seconds to TAI
to obtain UTC.  In general, without access to an
up to date table of leap seconds, it is not possible
to determine the difference between two UTC times,
since one or more leap seconds may lie between
them.  And, while I grant you they may not be
politicians or administrators, the actions of the
astronomers at the IERS are equally unknowable
more than a few weeks in advance.

I would argue that UTC, fixated as it is on the bobbles
of a spinning ball of rock, is yet another display format,
and that timestamps should be a form of Atomic Time.
At the very least, it should be recognized that UTC is
as unpredictable in its own way as Daylight Savings Time.

cheers,
Don Craig
Omneon Video Networks

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From: "John Stracke" <[email-masked]>
Date: Mon, 12 Nov 2001 09:26:08 -0500

Doug Royer wrote:

>Why not just specify that dates/times are RFC2445 compliant?
[...]
>We decided on ONE format for date time based on ISO-8601
>
>                YYYYMMDDTHHMMSS [+/- ...]

Not quite; RFC-2445 doesn't have the UTC offset.  (See section 4.3.5 of 
RFC-2445; at the bottom of page 35, it says, "The form of date and time with UTC offset MUST NOT be used".)  This was 
debated in the IMPP group; some suggested forgetting about timezones and 
just specifying that all timestamps had to be in UTC.  The counterargument 
was that knowing somebody's timezone offset helps you guess whether he's 
likely to be in the office, etc.

I did argue for using the pure-numeral form from RFC2445, until it was 
pointed out that we had to add the offset, which meant breaking 
compatibility with 2445 anyway.

/=============================================================\
|John Stracke                    |Principal Engineer          |
[email-masked]   |Incentive Systems, Inc.     |
|http://www.incentivesystems.com |My opinions are my own.     |
|=============================================================|
|I used to belong to a solipsism club, but I got bored & voted|
|everybody else out.                                          |
\=============================================================/