The best way to find about changes to the tz database is to subscribe to and monitor the tz mailing list: <a href="mailto:tz@elsie.nci.nih.gov">tz@elsie.nci.nih.gov</a>. Upcoming changes are typically discussed in advance of their release.<br>
<br>-Scott<br><br>On Fri, Dec 5, 2008 at 9:18 AM, Martin Barnes <span dir="ltr"><<a href="mailto:barnes@yahoo-inc.com">barnes@yahoo-inc.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Thanks Scott. Yes, I better understand the
provenance and status of the Olsen data now.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">I will look into the details to see the
efficacy of constructing the roll-up zones. Since they will be neither an Olsen
zone nor a CLDR metazone, we may have issues applying a name. The resultant
data will be predominantly Olsen with a few roll-ups but we would want to use
the Olsen name throughout. Reflecting on this, I think that it would be prudent
to align to the Olsen zones otherwise we might invite problems by associating a
place to an Olsen time zone name, when it actually belongs to a zone that has
been rolled-up into a "superzone" for which a different name has
been applied.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">I completely understand that the Olsen time
zones change from time to time. New ones are added and existing ones may be
modified. </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">My question is…is there anyway of
being notified when any changes occur to the tz database or is it a matter of systematically
checking?</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">-Martin</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
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<p><b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;" lang="EN-US">From:</span></font></b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;" lang="EN-US">
Scott Atwood [mailto:<a href="mailto:scott.roy.atwood@gmail.com" target="_blank">scott.roy.atwood@gmail.com</a>] <br>
<b><span style="font-weight: bold;">Sent:</span></b> 04 December 2008 20:05<br>
<b><span style="font-weight: bold;">To:</span></b> Martin Barnes<br>
<b><span style="font-weight: bold;">Cc:</span></b> <a href="mailto:tz@elsie.nci.nih.gov" target="_blank">tz@elsie.nci.nih.gov</a>;
<a href="mailto:tz@lecserver.nci.nih.gov" target="_blank">tz@lecserver.nci.nih.gov</a><br>
<b><span style="font-weight: bold;">Subject:</span></b> Re: Time Zone naming</span></font><span lang="EN-US"></span></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">The Olson zoneinfo database and CLDR are the closest thing that
presently exist to a standard for timezones, but they are de facto standards,
not de jure standards administered by any kind of official international
standards body.</span></font></p>
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<div>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">If it would be useful for your internal purposes, there is certainly
enough information in the Olson data to construct "roll-up" timezones
for yourself where the ISO-3166-2 code, GMT offset, and DST rules are all
presently identical. But as I mentioned below, you should expect such
entities to be rather fluid, and you should prefer to base your implementation
on the full fidelity Olson timezones. Such "roll-up" timezones
would be finer grained entities than CLDR metazones, since the only requirement
for metazones is that they must have the same display labels. Individual
Olson timezones within a CLDR metazone may have different DST rules and may
belong to different regions.</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<div>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Also, on the topic of future proofing, you should be prepared for the
fact that new Olson timezones are added from time to time whenever a subregion
of an existing zone changes its time definition independently of the rest of
that subregion. This happened during the recent timezone change in Argentina where
America/Argentina/Salta split off from America/Argentina/Cordoba. Any
Olson update could thus potentially require updates to your boundary
definitions.</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">-Scott</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">On Thu, Dec 4, 2008 at 10:48 AM, Martin Barnes <<a href="mailto:barnes@yahoo-inc.com" target="_blank">barnes@yahoo-inc.com</a>> wrote:</span></font></p>
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<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Thanks Scott. This is very useful insight.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">I am really only ever concerned with expressing the current
timezone for any given place and less worried by any need to relate to any
historical dates and times. </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Consequently it was my hope to use a sanctioned standard that
identified timezones as regions with the same political definition (ISO region
code), the same UTC offset and the same DST rules but that ignored any
historical context; whereby I could find and group all places that exhibited
and experienced the same current time behaviour (such as all the cities in
China belonging together).</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">But it appears that no such standard exists. Furthermore, and
as you point out in the Argentina
example, using the "pure" Olsen is recommended in view of the
frequent changes that are both "official" as decreed by governments
and "unofficial" as adopted by local usage. Having these zones
pre-defined as boundary map objects allows us a better degree of
future-proofing against changes to come. That is good enough for me.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">I guess if I need to I might be able to create relationships
between zones that behaved the same at any given point in time I might want to
look at the CLDR metazones, albeit with some caution.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">Thanks for your time and help.</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;">-Martin</span></font></p>
<p><font color="navy" face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial; color: navy;"> </span></font></p>
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<p><b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma; font-weight: bold;" lang="EN-US">From:</span></font></b><font face="Tahoma" size="2"><span style="font-size: 10pt; font-family: Tahoma;" lang="EN-US"> Scott
Atwood [mailto:<a href="mailto:scott.roy.atwood@gmail.com" target="_blank">scott.roy.atwood@gmail.com</a>]
<br>
<b><span style="font-weight: bold;">Sent:</span></b> 04 December 2008 17:24<br>
<b><span style="font-weight: bold;">To:</span></b> <a href="mailto:tz@elsie.nci.nih.gov" target="_blank">tz@elsie.nci.nih.gov</a><br>
<b><span style="font-weight: bold;">Cc:</span></b> <a href="mailto:tz@lecserver.nci.nih.gov" target="_blank">tz@lecserver.nci.nih.gov</a>;
Martin Barnes<br>
<b><span style="font-weight: bold;">Subject:</span></b> Re: Time Zone naming</span></font></p>
</div>
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<div>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
<div>
<div>
<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">To the
best of my knowledge, the Olson database itself does not define any kind of
"roll-up" timezones. The closest thing I am aware of is the
CLDR concept of "metazones" which group together Olson timezones that
share a common display string, like "Eastern Standard Time".
However, I believe these metazones can include timezones that have
different DST rules.</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Rather
than try to use "roll-up" timezones, from personal experience, I
would urge you to use the full Olson timezone list if possible. World
timezone rules are highly dynamic and change with surprising frequency.
And it is not uncommon for two Olson timezones to have the same GMT
offset and DST rules in one release of Olson, but then have different rules in
a future release. The example that you cite, Argentina, is an excellent example.
Until just a few weeks ago, all of Argentina was effective under the
same set of time zone rules, but when the central government decided to observe
DST this year, several of the states decided to remain in standard time.
An application that had assigned
"America/Argentina/Buenos_Aires" to everyone in Argentina
regardless of their actual Olson timezone would have broken.</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">Also note
that it can be useful to maintain the separate timezones if your application
needs to format and display historical dates and times, as in logging or
transaction history. Timezones that have the same GMT offset and DST
rules today may have had different rules in the past, and having the most
accurate timezone means you could display the historical records correctly as
well.</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;">-Scott</span></font></p>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
</div>
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<p><font face="Times New Roman" size="3"><span style="font-size: 12pt;"> </span></font></p>
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<p style="margin-bottom: 12pt;"><font face="Times New Roman" size="3"><span style="font-size: 12pt;">From: Martin Barnes [mailto:<a href="mailto:barnes@yahoo-inc.com" target="_blank">barnes@yahoo-inc.com</a>]<br>
Sent: Friday, November 28, 2008 11:48<br>
To: <a href="mailto:tz@lecserver.nci.nih.gov" target="_blank">tz@lecserver.nci.nih.gov</a><br>
Subject: Time Zone naming<br>
<br>
I have a question related to the accepted standard for expressing the<br>
"Olsen" name where multiple zones exhibit the same
"behaviour" in terms<br>
of belonging to the same country, having the same UTC offset and exactly<br>
the same DST rules.<br>
<br>
For example, it appears that all clocks within all locations within<br>
Argentina
will have the same time all year round. The 12 zones reveal<br>
the same behaviour. The same is true of China and a number of other<br>
countries.<br>
I have been aware of the concept of a "consolidated" or
"preferred" time<br>
zone which is a combined zone that takes the name of the most important<br>
location (eg. "America/Buenos_Aires" in the case of Argentina)<br>
<br>
Do these combined "super" zones exist? If so, is there information<br>
available that indicates how the individual zones roll up?<br>
<br>
My enquiry relates to a need to provide information that can identify<br>
the correct timezone for every place (city, postcode, county, state, etc<br>
etc) on earth via a back-end mapping service that calculates the spatial<br>
relationship between the place coordinate and the timezone boundary.<br>
I am looking to build up an accurate timezone boundary map essentially<br>
using existing map objects as building blocks.<br>
<br>
Many thanks<br>
-Martin Barnes<br>
______________________<br>
GeoData Manager<br>
Yahoo! Geo Technologies<br>
Geo Informatics team<br>
London</span></font></p>
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<p style="margin-bottom: 12pt;"><font face="Times New Roman" size="3"><span style="font-size: 12pt;"><br>
<br clear="all">
<br>
-- <br>
Scott Atwood<br>
<br>
Cycle tracks will abound in Utopia. ~H.G. Wells</span></font></p>
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<p style="margin-bottom: 12pt;"><font face="Times New Roman" size="3"><span style="font-size: 12pt;"><br>
<br clear="all">
<br>
-- <br>
Scott Atwood<br>
<br>
Cycle tracks will abound in Utopia. ~H.G. Wells<br>
<br>
</span></font></p>
</div></div></div>
</div>
</blockquote></div><br><br clear="all"><br>-- <br>Scott Atwood<br><br>Cycle tracks will abound in Utopia. ~H.G. Wells<br><br><br>