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June 2019

52 participants
32 discussions

Extend POSIX TZ to allow transition times outside 00-24 range, permanent DST
by Paul Eggert June 3, 2019

June 3, 2019

I recently proposed extending the POSIX spec for TZ strings. Please see: http://austingroupbugs.net/view.php?id=1252 This proposal is a modest one, as it doesn't specify TZ strings like 'America/Los_Angeles'. Instead it merely specifies the strings generated by zic and stored into TZif files. This includes strings like '<-03>3<-02>,M3.5.0/-2,M10.5.0/-1' which use times of day outside the 00-24 range, and strings like 'EST5EDT,0/0,J365/25' that represent permanent daylight saving time. This extension to POSIX TZ strings has already been specified in Internet RFC 8536 section 3.3.1 <https://tools.ietf.org/html/rfc8536#page-13> and I think it's a good idea to backport the extension to POSIX itself, as this will bless the common practice of taking the last line of a TZif file and using it as a TZ string on small platforms that lack room to store the TZif files. Please feel free to comment at austingroupbugs.net.

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[PROPOSED] Add an outline to tz-link.html
by Paul Eggert June 1, 2019

June 1, 2019

* tz-link.html: Add an outline, so that it’s more like theory.html. --- tz-link.html | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 92 insertions(+), 2 deletions(-) diff --git a/tz-link.html b/tz-link.html index e0d8cc8..85fc001 100644 --- a/tz-link.html +++ b/tz-link.html @@ -18,6 +18,46 @@ histories and planned futures are often recorded only fitfully. Here is a summary of attempts to organize and record relevant data in this area. </p> + <h3>Outline</h3> + <nav> + <ul> + <li>The <code><abbr>tz</abbr></code> database product and process + <ul> + <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li> + </ul> + </li> + <li>Uses of the <code><abbr>tz</abbr></code> database + <ul> + <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li> + <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li> + <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li> + <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li> + </ul> + </li> + <li>Related data + <ul> + <li><a href="#other-dbs">Other time zone databases</a></li> + <li><a href="#maps">Maps</a></li> + <li><a href="#boundaries">Time zone boundaries</a></li> + </ul> + </li> + <li>Timekeeping concepts + <ul> + <li><a href="#civil">Civil time concepts and history</a></li> + <li><a href="#national">National histories of legal time</a></li> + <li><a href="#precision">Precision timekeeping</a></li> + <li><a href="#notation">Time notation</a></li> + <li><a href="#see-also">See also</a></li> + </ul> + </li> + </ul> + </nav> + +<section> <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2> <p> The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a> @@ -88,6 +128,9 @@ Universal Time</a> (<abbr>UTC</abbr>). The database also records when daylight saving time was in use, along with some time zone abbreviations such as <abbr>EST</abbr> for Eastern Standard Time in the <abbr>US</abbr>.</p> +</section> + +<section> <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2> <p> The following <a @@ -148,6 +191,9 @@ specified by <a href="https://tools.ietf.org/html/8536">Internet The code also lets you read a <abbr>TZif</abbr> file and interpret timestamps for that location.</p> +</section> + +<section> <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2> <p> The <code><abbr>tz</abbr></code> code and data @@ -226,6 +272,9 @@ found in <a href="theory.html">Theory and pragmatics of the tz code and data</a> <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a> displays changes between recent <code><abbr>tzdb</abbr></code> versions. </p> +</section> + +<section> <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2> <ul> <li>The article @@ -239,6 +288,9 @@ href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonz literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the database's style.</li> </ul> +</section> + +<section> <h2 id="web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</h2> <p> @@ -270,6 +322,9 @@ calculates the current time difference between locations.</li> <li><a href="http://www.wx-now.com">Weather Now</a> and <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li> </ul> +</section> + +<section> <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2> <ul> <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s @@ -302,6 +357,9 @@ title="Extensible Markup Language">XML</abbr></a> format, and a variant uses <a href="https://www.json.org"><abbr title="JavaScript Object Notation">JSON</abbr></a> format.</li> </ul> +</section> + +<section> <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2> <ul> <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a @@ -439,6 +497,9 @@ source into text files, along with a runtime that can read those files. Tcl is freely available under a <abbr>BSD</abbr>-style license.</li> </ul> +</section> + +<section> <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2> <ul> <li>The <a @@ -497,6 +558,9 @@ package contains <a href="https://www.haskell.org">Haskell</a> code that parses and uses <abbr>TZif</abbr> data. It is freely available under a <abbr>BSD</abbr>-style license.</li> </ul> +</section> + +<section> <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2> <ul> <li><a href="https://foxclocks.org">FoxClocks</a> @@ -554,6 +618,9 @@ a macOS program. Its developers <a href="http://veladg.com/tzoffer.html">offer free licenses</a> to <code><abbr>tz</abbr></code> contributors.</li> </ul> +</section> + +<section> <h2 id="other-dbs">Other time zone databases</h2> <ul> <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a> @@ -582,6 +649,9 @@ Schedules Information Manual</a> of the International Air Transport Association gives current time zone rules for airports served by commercial aviation.</li> </ul> +</section> + +<section> <h2 id="maps">Maps</h2> <ul> <li>The <a href="https://www.cia.gov/index.html">United States Central @@ -609,6 +679,9 @@ much is time wrong around the world?</a> maps the difference between mean solar and standard time, highlighting areas such as western China where the two differ greatly. It's a bit out of date, unfortunately.</li> </ul> +</section> + +<section> <h2 id="boundaries">Time zone boundaries</h2> <p>Geographical boundaries between timezones are available from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a> @@ -683,6 +756,9 @@ for land and territorial waters only). A captain can change ship's clocks any time after entering a new time zone; midnight changes are common.</li> </ul> +</section> + +<section> <h2 id="civil">Civil time concepts and history</h2> <ul> <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-thr…">A @@ -704,6 +780,9 @@ time zone boundary.</li> <li><a href="http://statoids.com/tconcept.html">Basic Time Zone Concepts</a> discusses terminological issues behind time zones.</li> </ul> +</section> + +<section> <h2 id="national">National histories of legal time</h2> <dl> <dt>Australia</dt> @@ -790,6 +869,9 @@ Navy (SOHMA) publishes an annual <a href="http://www.armada.gub.uy/sohma/index.php/servicios/datos-astronomicos" hreflang="es">almanac (in Spanish)</a>.</dd> </dl> +</section> + +<section> <h2 id="precision">Precision timekeeping</h2> <ul> <li><a @@ -878,6 +960,9 @@ without Leap Seconds</a> gives pointers on this contentious issue, which was active until 2015 and could become active again.</li> </ul> +</section> + +<section> <h2 id="notation">Time notation</h2> <ul> <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data @@ -946,18 +1031,23 @@ any future changes to the rules. One should never set local time is nine hours ahead of <abbr>UT</abbr> and the time zone is called "<abbr>GMT</abbr>".</li> </ul> +</section> + +<section> <h2 id="see-also">See also</h2> <ul> <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li> <li><a href="tz-art.html">Time and the Arts</a></li> </ul> +</section> + +<footer> <hr> -<address> This web page is in the public domain, so clarified as of 2009-05-17 by Arthur David Olson. <br> Please send corrections to this web page to the <a href="mailto:tz@iana.org">time zone mailing list</a>. -</address> +</footer> </body> </html> -- 2.17.1

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