October 2021 - tz - lists.iana.org

[tz-announce] 2021d release of tz code and data available
by Paul Eggert via tz-announce Oct. 15, 2021

Oct. 15, 2021

The 2021d release of the tz code and data is available. This release reflects the following changes, which were either circulated on the tz mailing list or are relatively minor technical or administrative changes: Briefly: Fiji suspends DST for the 2021/2022 season. 'zic -r' marks unspecified timestamps with "-00". Changes to future timestamps Fiji will suspend observance of DST for the 2021/2022 season. Assume for now that it will return next year. (Thanks to Jashneel Kumar and P Chan.) Changes to code 'zic -r' now uses "-00" time zone abbreviations for intervals with UT offsets that are unspecified due to -r truncation. This implements a change in draft Internet RFC 8536bis. Here are links to the release files: https://www.iana.org/time-zones/repository/releases/tzcode2021d.tar.gz https://www.iana.org/time-zones/repository/releases/tzdata2021d.tar.gz https://www.iana.org/time-zones/repository/releases/tzdb-2021d.tar.lz The following convenience links are also available, although they may point to the previous release until the relevant caches are refreshed: https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz Links are also available via plain HTTP, and via FTP from ftp://ftp.iana.org/tz/releases with the same basenames as above. Each release file has a GPG signature, which can be retrieved by appending ".asc" to the above URLs. Copies of these signatures are appended to this message. This release corresponds to commit 4de3d7f2499328c97e652242a36fed9523741d12 dated 2021-10-15 13:48:18 -0700 and tagged '2021d' in the development GitHub repository at <https://github.com/eggert/tz>. Here are the SHA-512 checksums for the release files: dbd7e3df02a11676600aa7efa14592feb2ac9ab5807b0d395e0c29ff1ed4a31580120287df9fe0c65a78162157dcd31d9fbe90a2a93bfd891d59ae3668a3adda tzcode2021d.tar.gz e25e85679256cfa57072cc8902aad1ca1df5ddc4a06844ca38bd57c8b5ad386e38303654dc85525f4fb470a924db4deb3576827a14d3ff87f4a1c679414b95c9 tzdata2021d.tar.gz 6ccb3ed6ebf35643cb49d503f18b7c66957de098f41870fd14ac37489b0931abd6d3e7bf5c2797e69f56f44b31ff9f9068ffa40f5aa29260ecda9d0aac878103 tzdb-2021d.tar.lz Here are the GPG digital signatures for the release files: -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEfjeSqdis99YzvBWI7ZfpDmKqfjQFAmFp6ekACgkQ7ZfpDmKq fjQtmBAApD1Am4P0gbEECXOABxrnE258QrPRqPhupj45gW0kMD5BehW+yO2oIzOU zDmgLbWyG5CmbD2lSt2fq1mZKhfqYD2J4QJlwwiPGHriNKZZCVIQniXZVRFUzQz/ oObtIzNm5mgR6OUhWDcbzYZsa10eJ7HTMrDOGViZ7T1DyLj5yobSXqkC/Q/ZlEvM Vpnl9nDieey2GgXvobfpR+Bby6NB26Pojjab9Mbw9jyRtcvnf6GmdBn6v4aoDwKc ZUqcb9qjv7NXnN5o9nCUSK7/ad+RoVZJAVDe84Quj1Vn8ydfZ0/1+i6bF3mM6Bpi I3riuPKkv7AHW2iRgZPnnqH7U+X32gb55/+WleokkasZj7e8i1QjJW7L0b91YOHN USz1McquYNsh/n9IDph4Zw1tBpbmLYAy3HQPaR6OzO8fc9paw5nsoics/5fQ5WoZ 2T2EavJfa045XKxwzd57w9YthQgW27Ep6UMpVCEGjYCBfVt8MfmiB787apGJdeJj NeVaKfSfpE4PTWvrtfTXPCIVIbIhlA5UUXyhEBXrMJw/FVxf8rAHGi/zvmrgl48X iY/xMG4yWpUYwZqWG0NBeGE0tvj8Yj2NagWj/UnGXcte3MvgmjkFSnKhj+UZrcA+ 1ehgE8pGicWEl0xl7uW6uwJ1IgWBMHYIkxpslJdTru+nnfbBIaA= =Bvd6 -----END PGP SIGNATURE----- -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEfjeSqdis99YzvBWI7ZfpDmKqfjQFAmFp6ekACgkQ7ZfpDmKq fjTbSA/9HBEpib2dXzZg06u4WuVwFEbzu1AUblHm7I9PAzoxtTvJJqH0dMCrHDlj wldeHGclbBxLq8wF33Ajh7bvgISDhmjQCm/ux7nS0ctRnPkV4Pj2j6lsfk/gYVIB agFefLTTrdHaIrPxZ9TK7c63X+6HMfFDnE+nOrJXimls/gW/Xu/VeMDtngrCIoB3 JTSbPePbaSlA+NMn+RRhfb6jlw/Slbm7n5Zpf+VSZs2HN4+bNpHuFLbl5oMbPOrQ C+va/yKJXrNYroGOfIlz/ZnM24ZGDterLh9BBLe+zy3Ni+dhuH0x406C8zkZXSDu U1BZvHK3f84beSF0H1SbkGyjkfVSIol1o2p69mMdcyZzewng3n+MLB8lNxyMkmyk f8cTKviE0V+xoEe/yV8+0+uDhli+oLMudqNGy8eCRNgrnRkCsP513LMX73bagohQ xjtBd+cp2VSzhV4vXsJJE7mIwzofnZaGqdR/jyHND+4gx80TQo8Ftc29wRGbwCCI WU37r17EmcOPg+emOciIf8nYCPnIvKGBBZ0UcCEuvaZXXYhyg+2c82z7A+bIPZaS 6wQZhqptoWB07tJOMxcgCCV7I1fT8+GLlLLlJQXladooOa06mVzsFk8VlUX4PRl3 bIQGNgqRtoE/RnhbxgD0A4ToYUqdMvYzcoCGIGpg/4zmyFZWcaY= =NgZm -----END PGP SIGNATURE----- -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEfjeSqdis99YzvBWI7ZfpDmKqfjQFAmFp6esACgkQ7ZfpDmKq fjSsWg/+NCtwn4E06FCtkR08EV0R8uG4xI6HyQc8JsB5DiFkt+evge2Bu+De03y5 nUJ1eaWbg27MLMfdYI7q5tET9G5RRcFUSZx5Zpj+Bv++KHEz7QSB5ZajE2n2qi93 AkXtFEQn8n0sCKbxdpikiUtKyZbIhcBZkzpAVU3sDdphoLUJFI2YPUCwNL5sPnzH 9pI9/iXCvu1mDW0Mg+mdBO6BuMVmTZneSJ+qtWVRvDPBvWJu8vDr16YiNaTYXkX6 atnvTDmjc3RP5DAjFzItBjsZWcLfrWWQ9WezYXWGDmJS+ijxSH0eYAUfXdHESMMd ggNwlsYZumla1p8yGmHP7YkUynds2hZYV8ySCZhfaCjq/AYANs2hzYLIY5reQ6mJ XxRoGOECc2uCmIVwFjYAALghW0GnDAy6M/l+qgzSxAr92Y0GdlFSdv8yWvIBYPyg /gFKrS+IkLHPJEF5vcpxCpCJC2XR2lJLAzoAgLUc14kD5enmVUjJzia8CpKahq2S argJwtnUl+pZT5QLfOSC46jG2o+RnhSarPSNb21cs+eNnPMA31aXDIRrGDCJ6UXf nRAU1t7eq4bbb/cvEGgJ9ZCfoQpBhYT4QO8as4JXnzkHrB7PuUiqw2sOXixF6H46 MSKRQq/uWI6XiAbXpUDFh67EeH/U1YkR8mx67Uii6pcGLvK2ptM= =Brw7 -----END PGP SIGNATURE----- PS. If your tzdata parser does not yet support negative DST offsets or times past 24:00, or if it insists on a 'pacificnew' file that is no longer present, this release's data entries can be turned into a rearguard-format tarball that should work even with these older parsers. This is intended to be a temporary transition aid for these parsers. To generate a rearguard-format tarball, obtain the full distribution as described above, and run the command 'make rearguard_tarballs' on a development host. Or you can run 'make rearguard.zi' to generate a single file that can be fed directly to a parser that works like 'zic'.

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[PROPOSED 1/3] Document that -00 means local time is unspecified
by Paul Eggert Oct. 15, 2021

Oct. 15, 2021

* tzfile.5, zic.8: Document longstanding practice in time zone abbreviations. This better matches draft RFC 8536bis. --- tzfile.5 | 4 +++- zic.8 | 3 +++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/tzfile.5 b/tzfile.5 index 74564cb..e2f11b4 100644 --- a/tzfile.5 +++ b/tzfile.5 @@ -118,7 +118,9 @@ and serves as an index into the array of time zone abbreviation bytes that follow the .B ttinfo -structure(s) in the file. +entries in the file; if the designated string is "\*-00", the +.B ttinfo +entry is a placeholder indicating that local time is unspecified. The .B tt_utoff value is never equal to \-2**31, to let 32-bit clients negate it without diff --git a/zic.8 b/zic.8 index 3727922..89fc827 100644 --- a/zic.8 +++ b/zic.8 @@ -559,6 +559,9 @@ alphanumeric ASCII characters, .q "+" and .q "\*-". +By convention, the time zone abbreviation +.q "\*-00" +is a placeholder that means local time is unspecified. .TP .B UNTIL The time at which the UT offset or the rule(s) change for a location. -- 2.30.2

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Kiev >> Kyiv
by Pavlo Komendant Oct. 12, 2021

Oct. 12, 2021

Hello, Could you please amend the Ukraine capital in the time zone? Kyiv is the correct spelling of the Ukraine capital https://en.wikipedia.org/wiki/Kyiv Thank you! -- Pavlo

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Daylight Saving in Fiji Islands
by Jashneel Kumar Oct. 11, 2021

Oct. 11, 2021

Dear Support, Please note that there will be no daylight saving this year. Appreciate if the same can be reflected in your system to ensure that the time does not change. Looking forward to the confirmation. Regards, [New_VF_Icon_RGB_RED] Jashneel Kumar Manager Data Networks & Services Jashneel.Kumar(a)vodafone.com.fj<mailto:Jashneel.Kumar@vodafone.com.fj> Vodafone Fiji PTE Limited, 168 Princes Rd, Tamavua, Suva, Fiji Islands www.vodafone.com.fj<http://www.vodafone.com.fj/> Together we can [Vodafone] ________________________________ The content of this email including any attachments is confidential and may contain information that is proprietary and privileged. If you are not the intended recipient be advised that you have received this email in error and that any use, dissemination, forwarding, printing or copying of this email is strictly prohibited. If you have received this email in error please notify E-mail Administrator on info(a)vodafone.com.fj Please also destroy and delete this message from your system. Vodafone Fiji PTE Limited does not guarantee that this message is free from computer virus or any other defect. The reader accepts full responsibility for taking defensive and counteractive action needed to rectify the computer virus or other defects caused. Vodafone Fiji PTE Limited : Private Mail Bag, Suva, Fiji | Telephone : +679 3312000 | E-Mail : info(a)vodafone.com.fj Please consider your environmental responsibility before printing this e-mail [https://www.vodafone.com.fj//images/default-source/logo/logo-2x.png] Vodafone Fiji PTE Ltd <https://www.vodafone.com.fj/>

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Typo in zic(8) man page
by Jonathan Wakely Oct. 8, 2021

Oct. 8, 2021

The description of a RULES field in a zone line says: "giving of the amount of time to be added" The first "of" looks like a typo.

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Classifying IDs
by Stephen Colebourne Oct. 8, 2021

Oct. 8, 2021

Following on from the previous thread [1] I wanted to try and classify the IDs we have, which may or may not identify missing IDs. Again, please avoid talking about pre-1970 data at this point. Obsolete ------------ IDs that are obsolete and should never be used. They date from many years ago whe tzdb was just starting. Yet these still do appear in downstream UIs even today (of course UIs should not use the tzdb ID list, but in reality lots do). Examples: Portugal, NZ-CHAT, Navajo, Libya. Proposal: Provide 3-6 months notice, then move obsolete IDs to a new file "obsolete" which downstream projects are strongly encouraged not to include. (I would argue that the time has come to properly remove these IDs, which are very inconsistent in terms of which are provided and which not, eg Portugal, but not Spain) Deprecated, same location ------------------------------------ IDs that have been deprecated with a single clear alternative ID being provided. Both IDs represent the same physical location/city. Spelling changes: Asia/Katmandu (replaced by Asia/Kathmandu), Asia/Rangoon (replaced by Asia/Yangon) ID structure changes: America/Louisville (replaced by America/Kentucky/Louisville) Proposal: Ensure all of these are in `backward` Consider: Is there any way to move these IDs to the obsolete file? Maybe after 5 years? Or do we just accept backwards compatibility restrictions on these? Legally described mega-zones ----------------------------------------- IDs for locations where a federal or supra-national body defines rules, eg the EU or US DOT. Examples: US/Mountain, CET, WET Consider: Can we write down a rule to identify when something like this should be included? Then move the matching IDs to the main files (eg. are the EU and US DOT the only two examples here?) Regions ----------- IDs for abstract regions that have had the same wall clock since 1970. Examples: Europe/Berlin, America/New_York, Africa/Abidjan Proposal: Ensure all of these are in the main files. Consider: Should there be new IDs for each of these abstract regions to indicate they are a separate and distinct concept? eg. "Region/Berlin". (Maybe something to consider in future threads as it isn't clear what the benefit of doing so is without considering pre-1970 which I'm still trying to avoid) Non-region locations --------------------------- IDs for locations that are not region IDs. Each ID will have the same wall clock since 1970 as one of the region IDs. Examples: Europe/Oslo, Europe/Amsterdam, Atlantic/Reykjavik Consider: Can we write down a rule that covers which IDs are included here? And therefore when a new ID can be added to this set? If we can define a rule, then these can be split so rule-following IDs are in the main files and rule-breaking ones are in `backward` (although ideally they should be separate from the spelling changes). Obviously, we can say these IDs only exist for backwards compatibility, but that seems like a weak justification, and doesn't tackle the issue of when a new ID would be added to the list (which has been a point of tension). As is well known, I think the obvious rule is that the IDs follow the ISO-3166-1 standard (rule: one ID per ISO code, additional IDs may be added where clocks have diverged since 1970). Using ISO-3166 can be justified by IANA domain policy [2]: "We are not in the business of deciding what is and what is not a country. Instead, we employ a neutral standard maintained by the ISO 3166 Maintenance Agency. Our policy is to create new country-code top-level domains when the country or territory is listed on the ISO 3166-1 standard." As per the previous thread, these non-region location IDs are actively used in downstream business applications, and it is not OK that only works because tzdb happens to have IDs for backwards compatibility. There needs to be a better justification than that - these non-region locations need to be fully supported, with a consistent rule used to define what is and is not fully supported. Fixed/etc type rules -------------------------- IDs with a fixed offset Examples: GMT, UTC, Etc/GMT-9 Proposal: No change, retain in the main files unless a particular ID is considered obsolete or deprecated Are there any more classifications I've missed? Stephen [1] https://mm.icann.org/pipermail/tz/2021-September/030857.html [2] https://www.iana.org/help/eligible-tlds

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Downstream use of 2021c
by Philip Paeps Oct. 8, 2021

Oct. 8, 2021

Since the tzdata 2021c release removed most of the controversial link changes, I wonder how other downstreams feel about importing it. I spent some time this morning looking at the downstreams I know about. FreeBSD has 2021c in main but is still on 2021a plus Samoa and Jordan in the supported stable branches. Debian is in the same state as FreeBSD. NetBSD, OpenBSD and Ubuntu are on 2021a + Samoa and Jordan. Fedora is on 2021b. CentOS is on 2021a. A casual glance at other Linux distributions shows they are either on 2021a or 2021c. I am not familiar with their support models so I can't read anything into that. Python "pytz" seems to be on 2021c. Python "tzdata" seems to be in a similar state to FreeBSD, though I'm not sure I'm interpreting the release model correctly. I know Paul G is on this mailing list though. As far as I can tell, PostgreSQL is still on 2021a without modifications for Samoa and Jordan. Tom will correct me if I'm reading that wrong. I don't know enough about PHP, Java or any of the other well-known (let alone less well-known) downstreams to figure out what they're doing. This is looking terribly fragmented. Spare a thought for a hypothetical engineer tasked with debugging a Java application on Debian with some Python scripts on Fedora talking to a PostgreSQL database running on FreeBSD... While discussions on this list appear to have become more constructive, it looks like we're still lacking a clear consensus on the long-term direction. I feel that 2021c is a pretty reasonable compromise and would be willing to merge it to the supported FreeBSD releases. Is this something other downstreams would consider too? Alternatively, can we reach an interim consensus for a 2021d release that we'd all be willing to merge? Philip -- Philip Paeps Senior Reality Engineer Alternative Enterprises

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Use cases for source data
by Gilmore Davidson Oct. 8, 2021

Oct. 8, 2021

Stephen Colebourne's recent attempts to define requirements and use cases for tzdb got me thinking about the source data files. There have been several discussions over the years regarding the intended stability of the source format, separate from TZif binary files. These generally arise when the answer to a data query is "use this special compile-time flag". The most recent example is from Stephen at http://mm.icann.org/pipermail/tz/2021-September/030561.html The subtlety is in how the data set is consumed. While many downstream > projects use the makefile, not all do. A significant portion of > downstream users make use of the source files directly, with their own > parsers. ie. there is no ability to use a compile-time option. Those > parsers are not setup to use backzone even if it were a valid option > I think some of these discussions come about because there's disagreement about the intended use of the source files. The impression I've got from this list over the years is that the source files weren't intended to be a stable API; only the compiled TZif binary files were intended to be consumed downstream (and in later years, the .zi text representations). But many projects do use the source files as their primary interface, leading to tension when the format changes. So this is my attempt to list the use cases that people have for the source data files. This could prompt a wider discussion about what counts as a defined, stable interface for tzdb. Not every consumer of tzdb data is relying solely on the pre-compiled binary files. NOTE: This is a separate issue from the recent pre-/post-1970 data discussions. I'm trying to stay away from wading into that topic. ----------------------- Consumers of the source data text files: 1) The zic compiler for producing TZif binary files and .zi text files in an official tzdb release. 2) People reading the file comments to understand the history of certain zones. 3) Libraries/projects that need to parse/compile the data into a different representation than that provided by zic. This is often, but not exclusively, to preserve the distinction between Link and Zone entries, either for API or data compression reasons. 4) Data analysis or visualisations that care about knowing the higher-level Rule definitions ("transition on the last Sunday of October every year") rather than the exact transition timestamps for each year. 5) IDE or text editor plugins that provide syntax highlighting for the source files. All of these are based just on my own experiences and from lurking on this list. Any corrections/additions are welcome.

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Re: [tz] On ISO country for timezones (Re: Classifying IDs)
by dpatte Oct. 7, 2021

Oct. 7, 2021

I believe you are missing an important part of this discussion.There is a strong need for a repository of pre 1970 data, especially for historical research applications. As this is the only tz database, tz has also become the main database for this older data.For any populated place on earth researchers need such a repository. If I want to add the pre 1970 tz history for Ottawa Canada where should it be stored? Since it is called tz, and it also has other pre 1970 data, tz seems the appropriate place.But if no simple method of adding open-ended historical data is negotiated here, then the only other option is to fork tz and work on it as a separate project.Secondly, since the number of locations that could eventually be supported in a historical tz database is potentially very large, it cannot not be micromanaged, and this suggests that each historical zone should use an international standard for naming - iso - for simplicity and clarity.Canada/Ontario/OttawaAre we going to have two tz databases, or just one. That is the question here.Sent from my Galaxy -------- Original message --------From: Steffen Nurpmeso via tz <tz(a)iana.org> Date: 2021-10-07 09:35 (GMT-05:00) To: Stephen Colebourne <scolebourne(a)joda.org> Cc: tz(a)iana.org Subject: Re: [tz] On ISO country for timezones (Re: Classifying IDs) Stephen Colebourne wrote in <CACzrW9Cau-q2e+yoBcg=7Rztu19zZN582Xca9ZMYbz=H_0iOpw(a)mail.gmail.com>: |On Thu, 7 Oct 2021 at 07:08, Watson Ladd via tz <tz(a)iana.org> wrote: ... |I agree with backwards compatibility. The primary concern here is |whether an ID is considered deprecated or not.IDs shall be stable and not change at all. At maximum they shouldbe moved to backward, for example if a zone is renamed (which mayhappen for example for Ukraine in a not too distant future, ifthat is still necessary then, and it looks as if it would be).I would always have been all for making infinite stability of IDsa documented assertion.Even if not, your "six months" claim is nothing but an aggressivestatement. I think this entire thread is shadowboxing and noisefor nothing.Looking at the interface of your JAVA framework i think getID()should simply return the correct ID, which may be a link if it isone, and just in case this is not what getID() already returns.In my opinion there are only two problems with IANA TZ and howPaul Eggert manages it as a maintainer. That is the same PaulEggert who contributes to this software since 1995, an astonishing26 years. Corroding the maintainership with a continuous streamof noise is disgusting.The first is combining of datasets to equal-post-1970 bundles,which is going on for many years. But the data is there, it is inbackzone, and everybody can easily install a complete TZ DB onone's own request. Yet noone did, even though many packagers areon this list. This is schizophrenic. But maybe it is onlybecause of black and yellow people do not matter as much as someblue-eyed white people from northern Europe, which does not trulycome as a surprise given the audience who possibly reads this now,and given the fact that colonianisation ended only about 55 yearsago, and de facto was only turned from armed political to armedmaterial oppression.The second is that documentation did not follow suit the codeimprovements, as has been recently shown for tzselect(8) and the-t option. That tzselect(8) uses the administrative zone1970.taband not the end-user-preferrable zone.tab is a different thing.If you want to enforce upon the maintainer of the TZ database thatthe pre-1970 data is joined back into the normal data, or that"backzone" is splitted into "backzone" and "unreliable", and/orthat "backzone" is included by default, and/or that "ZFLAGS='-r@0'" is made default, then create a thread and try to gain enoughhums, but please stop this subversion by spreading uncertainty andthat even upon topics which never were under discussion as far asi know, and i also read this list for a decade now.It must anyway be said it was nicer once i only had thedistribution and did not know about the list :)Ciao from Germany,--steffen||Der Kragenbaer, The moon bear,|der holt sich munter he cheerfully and one by one|einen nach dem anderen runter wa.ks himself off|(By Robert Gernhardt)

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TZDB use cases
by Stephen Colebourne Oct. 7, 2021

Oct. 7, 2021

In this thread I want to try and capture the *requirements* for the project from the perspective of a downstream user. Given this, we may then have a chance to analyse whether the project needs a change of rules. NOTE: The discussion below is not a proposal, nor does it seek to explore which locations get pre-1970 data. Lets keep that for another thread. -------- 1) "What is the time now?" To answer this question you need a dataset that records the current timezone rules for each region in the world. Over time that data will naturally build up to form a historic record. To aid the project, a 1970 rule has been adopted for data management. In some parts of the world, clocks have agreed since 1970 across large parts of a continent. In other parts of the world, different parts of the same country have had different rules since 1970. Viewing the data through a post-1970 lens splits the planet into regions where clocks have agreed since 1970. Some of these regions are quite abstract, for example the region including Iceland, Ivory Coast, and St Helena. An abstract region would need to be split if one of the parts of the region changed its timezone rules. If a user had previously selected to follow one of these abstract regions, they might have to change their timezone settings. For example, if a user in Iceland selected their abstract region by the recommended ID based on the largest city they would get `Africa/Abidjan`, but if the Ivory Coast changed their rules, users in Iceland would have to change their selected timezone. The minimum set of IDs is one ID for each abstract region. The current ID scheme selects the largest city in the abstract region. My interpretation: * An abstract region should theoretically have an ID separate to the IDs of the cities/countries in the region * Trying the ID of the abstract region to the largest city in the region is prone to failure if that city changes timezone rules but the rest of the abstract region stays the same. * An abstract region ID would naturally have no pre-1970 data, as it doesn't define data in a single city/location. * The alternative is to encourage users to use their local city, which means that IDs like Europe/Amsterdam and Europe/Oslo cannot be deprecated -------- 2) "What was the time at some instant in the past?" The project can answer this question pretty reliably for dates from 1970 onwards because of the data set in #1. The project can never realistically answer the question reliably or accurately before 1970 for *all* locations. For example, timezone rules were entirely local in the US for about 20 years, meaning that hundreds of entries would be needed to correctly capture the data. In addition, much of the historic data globally is unknown and not viable to research, even if someone wanted to do so. It is possible to research and record historic timezone rules for *some* locations. Europe/London being one example. The project generally operates on the basis that if an ID exists, historical data can be recorded against it, although which file that data lives in has varied over time. IDs are generally not created solely to document historic data. There is no minimum set of IDs for this use case - the set of possible IDs is unbounded. My interpretation: * The majority of pre-1970 data isn't much use * Some pre-1970 data is high quality, and almost certainly relied upon (eg Europe/London) * Without a massive increase in scope the best that can be done pre-1970 is to record data against IDs created for some other reason. -------- 3) "An event will happen at this time in the future" If an end-user wants to store an event in the future, eg. a one hour meeting next month, the correct approach is to store the date, time and zone ID, not the offset (which is not yet known for certain).Even if the local timezone authority changes the tz rules between now and the event, the time of the event is still correct. https://stackoverflow.com/questions/19166995/java-calendar-date-and-time-ma… For this approach to work, the ID that is stored must be aligned with the timezone authority. Business contracts are frequently written to describe future events. For example, payment must be made by 2pm Paris time on a given date. The minimum set of IDs for this use case is one ID per timezone authority. This is typically the country but not necessarily, examples being decisions devolved to states/nations etc. My interpretation: * Using TZDB IDs for future events/contracts is very widespread * In most parts of the world, this requires one ID per country, in some parts of the world additional IDs would ideally be needed such as per state in the US * One ID for each ISO country (as was the guideline in the past) is a reasonable minimum expectation of end users * While one might argue IDs for future events are not TZDBs problem, I believe the reality is that they are because usage in this way is already very widespread -------- 4) "An event will happen at this time in the future relative to a shared/common definition" Some future events are declared relative to a definition that is supra-national or federal. For example, US Mountain, US Pacific, EU Central etc. A TV show might be defined to air at 8pm Mountain Time in one months time. It will air at that time regardless of whether any of the states that are currently on Mountain Time change to Pacific Time. For example, even if Denver (and Colorado) moved to Pacific Time or stopped following DST, Mountain Time would still exist and the TV show would still air at 8pm Mountain. The minimum set of IDs for this use case is one ID per shared/common definition. These IDs are not full aliases for a country or city ID, although they may currently share data. To support this use case, these IDs cannot be deprecated. My interpretation: * Some shared zone IDs are distinct and separate enough to warrant a full ID * US Mountain time is not the same as Denver time when considering the future, the IDs could diverge * In TZDB terms, the Link from US/Mountain to America/Denver is fine to define the data, but US/Mountain should not be considered deprecated as it has a real and distinct meaning separate from America/Denver * It would be useful to agree what the criteria for including these shared/federal rules is. -------- 5) "Data should be backwards compatible" The project has various associated downstream projects. Many of these have an expectation of backwards compatibility. This compatibility extends to the binary format, the source format, and the data contained within. This use case wants to see the project just continue with the data it has, enhancing it over time. The project has a pretty good record in terms of not removing IDs. For example, IDs exist for "Portugal" and "Poland", but not "Italy" or "Spain" simply because they were defined once upon a time. My understanding is that IDs in the `backward` file represent deprecated IDs that should not be used going forward. Yet, downstream projects focussed on backwards compatibility will generally use the `backward` file in full. The minimum set of IDs for this use case is the set of IDs that existed in the previous release. My interpretation: * Many users care about compatibility * The current IDs are not going away * Inconsistency has existed in TZDB for many years, see "Portugal" vs "Spain" - no one wants to fix that * It is hard at present to identify IDs that are deprecated because of proper aliasing, such as spelling changes, vs those where the ID is a real location but its TZDB status has been reduced. * Change may be possible with a long notice period --------- Please note that the above is not a proposal, but an exploration of the design space. If you have any use cases I've missed feel free to write them up. thanks Stephen

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