Subject: [Tzdist] draft-ietf-tzdist-service/ 3.2. Time Zone Aliases

From: Tobias Conradi <[email-masked]>
Date: Tue, 23 Sep 2014 14:11:43 +0200

http://datatracker.ietf.org/doc/draft-ietf-tzdist-service/

"A time zone data distribution service needs to maintain time zone
   alias mapping information, and expose that data to clients as well as
   allow clients to query for time zone data using aliases."

Whether there exist aliases at all is depending on the design of the
specific TZDB that is supported.

The IANA TZDB does use aliases, but other TZDBs may avoid identifier
duplication.

-- 
Tobias Conradi
Rheinsberger Str. 18
10115 Berlin
Germany

http://tobiasconradi.com

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From: Eliot Lear <[email-masked]>
Date: Tue, 23 Sep 2014 15:06:21 +0200

Hi Tobias,

> The IANA TZDB does use aliases, but other TZDBs may avoid identifier

If the concept of an alias exists within the database, then it needs to
be supported by the protocol.  Our charter also specifically does call
out the TZ Database which has this concept.  This text was the result of
earlier discussions.  Absent new information, I'd like to not revisit
this issue.

Eliot

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From: Lester Caine <[email-masked]>
Date: Tue, 23 Sep 2014 14:20:42 +0100

> The IANA TZDB does use aliases, but other TZDBs may avoid identifier

It is a fact that there may be no correlation between a physical
location and a single set of data. It does seem to be assumed that for
every location there WILL be a single set of data? And for a truncated
view this may well be the case, but for historic data which set of data
being used may have changed. Even currently 'alias mapping information'
going back in time may result in a different set of data being used by a
location even if only a change of LMT setting. It was this expansion of
aliases which the 1970 truncation rules on TZ were intended to prevent
and at one time it was even proposed deleting what are now classified as
duplicate aliases. Fortunately while that has been put on hold, and the
backzone material retains the culled data, but this just causes
confusion in general!

I commented on 'passing the buck' previously, and this is one of those
areas where we DO need a clean and concise definition of what a time
zone is so that we know what is being provided even by the TZ database.
My comment about using the generic rules rather than expanded 'alias'
rules has relevance here since a location mapping service would simply
identify the correct sequence of physical time offsets and newer generic
rules ... a 'time zone' is used by a location ... a location is not a
time zone.

-- 
Lester Caine - G8HFL
-----------------------------
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From: Tobias Conradi <[email-masked]>
Date: Tue, 23 Sep 2014 15:52:30 +0200

On Tue, Sep 23, 2014 at 3:20 PM, Lester Caine <[email-masked]> wrote:

> zone is

According to the glossary

http://www.ietf.org/mail-archive/web/tzdist/current/msg00513.html

a time zone is "A description of the historical and predicted timekeeping
      practices of a collection of clocks that are intended to agree"

So, a text could be a time zone if it is such description.

Alias at
http://dictionary.reference.com/browse/alias
is "a false name used to conceal one's identity"

Then a "time zone alias" could be a name for a description of practices?

So, an ISTC (International Standard Text Code) could be a time zone
alias? E.g. if the text that it identifies describes timekeeping
practices for all tower clocks in Berlin?

> a 'time zone' is used by a location
a location uses a description of practices? I thought descriptions are
used by persons.

> ... a location is not a
That depends on the definition of location. When having a "time zone"
defined as "description" I would not be surprised that a definition of
"location" would bring up one that has never been seen for that term
before.

-- 
Tobias Conradi
Rheinsberger Str. 18
10115 Berlin
Germany

http://tobiasconradi.com

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From: Rob Seaman <[email-masked]>
Date: Tue, 23 Sep 2014 06:58:34 -0700

On Sep 23, 2014, at 6:20 AM, Lester Caine <[email-masked]> wrote:

> every location there WILL be a single set of data?

Could also be no data (the high seas), or more than one set:

	http://articles.latimes.com/2009/mar/31/world/fg-china-timezone31

> zone is so that we know what is being provided even by the TZ database.

This is desirable, but different stakeholders may rely on differing implicit definitions.  The best you can hope for is a clear statement of what IETF means by the term.

> ... a 'time zone' is used by a location ... a location is not a time zone.

Indeed.  And populations in close proximity may assign different timezones to the same or closely neighboring locations.  For example, Holbrook to Flagstaff, Arizona is a distance of 90 miles on the interstate highway.  During the summer if you instead make the trip via Tuba City you would have to change your watch six times passing between four nested timezone variations:

	http://blog.maps.com/wordpress/maps/why-do-we-reset-our-clocks-a-brief-history-of-daylight-savings/

(scroll to the bottom)

Rob Seaman
National Optical Astronomy Observatory
Tucson, AZ

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From: Lester Caine <[email-masked]>
Date: Tue, 23 Sep 2014 15:37:39 +0100

On 23/09/14 14:58, Rob Seaman wrote:
> Could also be no data (the high seas),

That depends on being English or French ;)
Maritime time is what started most of this anyway?
That a ship may use one time zone or another is perfectly acceptable.
Cruise ships seem to be a law unto themselves anyway, but knowing which
time zone to use is dictated by the ships captain rather than the location.

> or more than one set:

Perfect example ... the time zone data may be well defined but jst which
one is used may depend on more than simple location ...