February 2001 - tz - lists.iana.org

RE: What is a time zone?
by Olson, Arthur David (NCI) Feb. 17, 2001

Feb. 17, 2001

The existing public-domain time zone stuff lets you know how to represent local time if you provide the identity of the set of rules that apply. Recent mail has dealt with the matter of handling things such as geographic locations or phone system area codes. My sense is that layered software is the way to go. The bottom level turns a time-zone identifier into a representation of the rules that apply. Built on top of this are packages that take different forms of input (phone system area code, geographic location) and deliver up time-zone identifiers. The existing time-zone stuff is a bottom level. And there might be multiple higher levels--for example: topmost geographic location to phone system area code middle phone system area code to time zone identifier bottom time-zone identifier to rules that apply The organization of the higher levels would, of course, be immaterial to what goes on at the bottom level. A consideration in determining the time-zone identifiers to use in such a setup is the independent usability of the bottom level. The existing time zone stuff uses identifiers of the form big-geographic-region/city; this allows some meaningful applications (such as setting the local time to be used on a computer) without recourse to a higher level (proof by existence). There are other considerations as well (technological, political, technological, astrological...). And determining what to use as a time-zone identifier ought not be done in a vacuum: if the same identifier can be used for other purposes, we've simplified our lives.

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time zone geography
by Chuck Ellis Feb. 16, 2001

Feb. 16, 2001

I have worked on the subject of time zone geography in the past (with tz's data) and actually had gotten thru to the point of generating a low-scale (~ 1:2MM) world map of the (I believe in 1998 it was 305) unique geographic zones. Since the zones were boundary objects in a GIS application, DST rules were applied dynamically, so the actual unique boundary count changed depending on date and time. I interject myself into the list discussion at this point because geography is simply a special case in relation to any proposed tz-focused software application that is going to deal with it. Even the issue of whether an area code is in a particular time zone or not is non-trivial. "Area Codes" are a North American 'thing', specifically defined by the North American Numbering Plan (NANP, managed by Bell). The rest of the world uses a Country-Code/City-Code system. The point is relevant because the geography of NANP boundaries is reasonably well characterized into a contiguous set of boundary polygons, with some "overlays" of identical boundaries where such overlays exist. Therefore, what particular zone(s) are relevant to a time zone in the NANP system is a matter of quite precise geographic calculation: one overlays the area code boundary map onto the time zone boundary map, and reads back the relevant "object contains" and/or "object intersects" set of time zones. Perfectly likely that a NANP area code completely contains one tz (e.g., Indianapolis is the summer), and intersects in some proportion another (e.g., Chicago). In the rest of the world, it can get quite messy. City-Code boundaries are well-characterized in some countries (e.g., France), and utterly nonexistent in many more (e.g., Burundi). The best one will be able to do in these situations is to default to using a "centroid" (the approximate geographic center of a city or town) and simply reading back which tz those coordinates fall within. The larger issue is not, of course, area codes, but any geography. It's a long list, but is best organized into three natural classes of geometric objects-- points, lines (including polylines), and polygons (including closed curves). The most relevant polygons include political, civil, administrative, telcomm, marketing, cadastral (property), statistical, media and those from the natural sciences. Common examples are country/state, city, area code, Designated Marketing Area, broadcast signal surfaces, lakes, zip codes, etc. Line and polyline objects can include roads, rivers (depending on resolution and scale), rail, power and fence line, pipeline, faultline and many more. Point objects are even more numerous, but certainly start with a "gazeteer", or roster of city/town names and coordinates, and progress to physical objects (towers, buildings, wells, etc.) to the very spot you happen to be sitting at right now. It is reasonable to imagine almost any type of geographical object, and want to know-- "What time zone is it in ?" Any application that is going to answer this question does not need to reinvent the wheel and write code to analyze overlaps, intersections, contains or any other "standard" GIS (geographical information system) function, including simply rendering and printing. There are hundreds of GIS systems out there, and even more code tools to embed particular functions into "your" app. The real challenge is on two ends of the issue-- the time zone "map", such as needs to be created and maintained; and the "map" (or at least digital embodiment therein) of whatever geographic object(s) are to be compared against the time zone map. For example, to determine what time zone(s) a particular NANP area code lies in, we need a digital map of that area code, the digital map of the world's time zones, and any GIS software or application containing such functions. Digital maps of nearly everything and everywhere are pretty widely available. Most addresses can be quickly "geocoded", or assigned lat/lon coordinates-- which is a digital map of that address. Since almost any geographical object's map can be purchased or downloaded with relative ease (cost notwithstanding), the map that is missing is, of course, a current time zone map. As I have pointed out in this discussion some years ago, a complete and current time zone map holds enormous power and utility for many (if not most) of the readers of this discussion list. One can purchase the GNIS CD-ROM containing the official names and coordinates of over 4 million cities, towns, villages, places, etc. in the world; overlay this file on a world time zone map; and in approximately 2 to 3 minutes on a Pentium PC, assign the proper time zone to all 4 million places. It's a little more complicated with boundary (polygon) overlays, but you get the idea. I am willing to devote some more time to trying to create the fundamental tz map that is needed for the generalized application that Arthur is discussing, but it is too much for one person alone, and really requires an organized effort to maintain its currency against the ever-changing tz database. I would ask at this time if there are any volunteers out there with some GIS or database skill that would help, and if there are enough responses, perhaps we could proceed to a more permanent group of focused volunteers. Initially, we would not tackle historical zones-- the current stuff is hard enough to keep track of ! Chuck Ellis chuck_ellis(a)msn.com -----Original Message----- From: Olson, Arthur David (NCI) [mailto:olsona@dc37a.nci.nih.gov] Sent: Friday, February 16, 2001 3:48 PM To: tz (E-mail) Subject: RE: What is a time zone? The existing public-domain time zone stuff lets you know how to represent local time if you provide the identity of the set of rules that apply. Recent mail has dealt with the matter of handling things such as geographic locations or phone system area codes. My sense is that layered software is the way to go. The bottom level turns a time-zone identifier into a representation of the rules that apply. Built on top of this are packages that take different forms of input (phone system area code, geographic location) and deliver up time-zone identifiers. The existing time-zone stuff is a bottom level. And there might be multiple higher levels--for example: topmost geographic location to phone system area code middle phone system area code to time zone identifier bottom time-zone identifier to rules that apply The organization of the higher levels would, of course, be immaterial to what goes on at the bottom level. A consideration in determining the time-zone identifiers to use in such a setup is the independent usability of the bottom level. The existing time zone stuff uses identifiers of the form big-geographic-region/city; this allows some meaningful applications (such as setting the local time to be used on a computer) without recourse to a higher level (proof by existence). There are other considerations as well (technological, political, technological, astrological...). And determining what to use as a time-zone identifier ought not be done in a vacuum: if the same identifier can be used for other purposes, we've simplified our lives.

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RE: etcetera patch
by Jesper Nørgaard Feb. 16, 2001

Feb. 16, 2001

Okay, that was much better. It is still complicated matter, but at least it was so clear that I got encouraged to make another suggestion for how to formulate it. I thought that the essence of "what many people expect" got lost in the examples. How about this: # We use POSIX-style signs in the Zone names and the output abbreviations, # even though this is the opposite of what many people expect. # POSIX has positive signs west of Greenwich, while most people expect # positive signs east of Greenwich. For example, TZ='Etc/GMT+4' corresponds # to 4 hours behind UTC (i.e. west of Greenwich) which many people would # expect to see as GMT-4. In Draft 5 of the next version of POSIX, the angle # bracket notation (which is not yet supported by the tz code) allows for # TZ='<GMT-4>+4'; if you also want abbreviations that conform to ISO 8601 # you can use TZ='<-0400>+4'. Thus the expected offset is kept within the # angle bracket (and not used for calculation) while the POSIX sign is kept # outside the angle bracked (and used for calculation). Regards, Jesper Nørgaard Welen Email: jnorgard(a)Prodigy.Net.mx Programador/Analista CIMMYT - Centro Internacional de Mejoramiento de Maíz y Trigo Dirección: CIMMYT Int. c/o Jesper Nørgaard Km. 45, Carretera México-Veracruz El Batán Texcoco, Edo. de México CP 56130 MEXICO Tel.: +52 (5) 58-04-20-04 ext. 1374 Fax: +52 (5) 58-04-75-58 Tel. Casa: 53-10-05-95 ó 53-10-97-78 CIMMYT home page: http://cimmyt.cgiar.org Check out my free program World Time Explorer: http://timezone50.homepage.com ---------- From: Paul Eggert[SMTP:eggert@twinsun.com] Sent: Jueves 15 de Febrero de 2001 11:28 To: jnorgard(a)Prodigy.Net.mx Cc: tz(a)elsie.nci.nih.gov Subject: Re: etcetera patch > Date: Wed, 14 Feb 2001 22:21:35 -0600 > From: =?iso-8859-1?Q?Jesper_N=F8rgaard?= <jnorgard(a)Prodigy.Net.mx> > Resent-From: tz(a)elsie.nci.nih.gov > > "internal-style signedness" and "zic style"?? Reading the below utterings > just makes me bounce of the wall and scratch my head (but not at the same > time :-). OK, here's a draft rewording that I hope doesn't leave as many marks on your wall (and your head :-). # We use POSIX-style signs in the Zone names and the output abbreviations, # even though this is the opposite of what many people expect. # For example, TZ='Etc/GMT+4' corresponds to 4 hours behind UTC # (i.e. west of Greenwich); it is equivalent to TZ='GMT+4', # except that it uses the abbreviation "GMT+4" # whereas TZ='GMT+4' uses the misleading abbreviation "GMT". # TZ='Etc/GMT+4' is equivalent to the TZ='<GMT+4>+4' of Draft 5 of the next # version of POSIX, but the angle-bracket notation is not yet # supported by the tz code. With the Draft 5 notation, people who # prefer the traditional sign in abbreviations (where positive numbers # are east of Greenwich) can use TZ='<GMT-4>+4'; if they also want # abbreviations that conform to ISO 8601 they can use TZ='<-0400>+4'.

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RE: etcetera patch
by Jesper Nørgaard Feb. 16, 2001

Feb. 16, 2001

"internal-style signedness" and "zic style"?? Reading the below utterings just makes me bounce of the wall and scratch my head (but not at the same time :-). Even though I have been on this mailing list for some time, I still have no idea what you are talking about. Wouldn't some plain english be in place here? Sorry for the grouch. It was actually meant to be constructive criticism. If you can't describe this without using a lot of words, insert examples in the sentences right after the keywords. Regards, Jesper Nørgaard Welen Email: jnorgard(a)Prodigy.Net.mx Programador/Analista CIMMYT - Centro Internacional de Mejoramiento de Maíz y Trigo Dirección: CIMMYT Int. c/o Jesper Nørgaard Km. 45, Carretera México-Veracruz El Batán Texcoco, Edo. de México CP 56130 MEXICO Tel.: +52 (5) 58-04-20-04 ext. 1374 Fax: +52 (5) 58-04-75-58 Tel. Casa: 53-10-05-95 ó 53-10-97-78 CIMMYT home page: http://cimmyt.cgiar.org Check out my free program World Time Explorer: http://timezone50.homepage.com ---------- From: Paul Eggert[SMTP:eggert@twinsun.com] Sent: Miércoles 14 de Febrero de 2001 3:17 To: alex(a)agsm.edu.au Cc: tz(a)elsie.nci.nih.gov Subject: Re: etcetera patch > Date: Wed, 14 Feb 2001 18:03:54 +1100 > From: Alex LIVINGSTON <alex(a)agsm.edu.au> > ># We use POSIX-style signedness in the names and output, > ># internal-style signedness in the specifications. > > What is "internal-style signedness"? Would your "average" tz user know? How? It's zic style. I'll change "internal" to "zic-input". > ># ... With the Draft 5 notation, people who > ># prefer the traditional time zone sign can use TZ='<GMT-4>+4'. > > What is "the traditional time zone sign"? The sign where positive numbers are east of Greenwich. I'll change the wording here too. > What about UTC as opposed to GMT? The existing zone names all use "GMT" so I think it's better to use GMT in the examples. > Might you also say "people who prefer ISO-8601 compliant time-zone > signs can use TZ='<UTC-04:00>+4' instead"? That doesn't conform to either ISO 8601 or to d5. ISO 8601 does not allow the 'UTC'; d5 does not allow the ':'. However, TZ='<-0400>+4' would conform to both, I think; I'll add that example too. Thanks for your comments.

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please tell me when
by MarieATOKC＠aol.com Feb. 15, 2001

Feb. 15, 2001

the time is that we change the clocks ahead for spring ? thank you ..Marie

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FW: ZoneInfo.java
by Olson, Arthur David (NCI) Feb. 14, 2001

Feb. 14, 2001

Stuart D. Gathman is not on the time zone mailing list; direct replies appropriately. --ado -----Original Message----- From: Stuart D. Gathman [mailto:stuart@bmsi.com] Sent: Wednesday, February 14, 2001 5:50 PM To: tz(a)elsie.nci.nih.gov Subject: ZoneInfo.java You might wish to link to http://www.bmsi.com/java/#TZ It is a Java language reader for tz format zoneinfo files. -- Stuart D. Gathman <stuart(a)bmsi.com> Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flamis acribus addictis" - Mozart background song for the Microsoft "Where do you want to go from here?" commercial.

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ZoneInfo.java
by Stuart D. Gathman Feb. 14, 2001

Feb. 14, 2001

You might wish to link to http://www.bmsi.com/java/#TZ It is a Java language reader for tz format zoneinfo files. -- Stuart D. Gathman <stuart(a)bmsi.com> Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flamis acribus addictis" - Mozart background song for the Microsoft "Where do you want to go from here?" commercial.

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Feb. 14, 2001

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Re: etcetera patch
by Paul Eggert Feb. 14, 2001

Feb. 14, 2001

> Date: Fri, 9 Feb 2001 18:20:39 -0800 (PST) > From: Robbin Kawabata <Robbin.Kawabata(a)eng.sun.com> > > I think etcetera is OK.... On second thought you're probably right. This stuff is so obsolete now, changing it would probably add to confusion rather than subtracting it. > Note the comments in the file itself: > > # We use POSIX-style signedness in the names and output, > # internal-style signedness in the specifications. > # For example, TZ=Etc/GMT+4 corresponds to 4 hours _behind_ UTC; > # it is equivalent to TZ=GMT+4, which is implemented directly as per POSIX. Those comments are not quite right either, and they added to my confusion. TZ=Etc/GMT+4 is not exactly equivalent to TZ=GMT+4, because they result in different abbreviations. How about if we change the above comments to be something like this instead? # We use POSIX-style signedness in the names and output, # internal-style signedness in the specifications. # For example, TZ=Etc/GMT+4 corresponds to 4 hours _behind_ UTC; # it is equivalent to TZ=GMT+4, except that it uses the abbreviation "GMT+4" # whereas TZ=GMT+4 uses the misleading abbreviation "GMT". # TZ=Etc/GMT+4 is equivalent to the TZ='<GMT+4>+4' of Draft 5 of the next # version of POSIX, but the angle-bracket notation is not yet # supported by the tz code. With the Draft 5 notation, people who # prefer the traditional time zone sign can use TZ='<GMT-4>+4'.

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Fw: What is a time zone?
by Thomas Carey Feb. 14, 2001

Feb. 14, 2001

great analysis, david. thanks. I think you hit the nail on the head about differences in approach to the problem. Of course in practical terms a simple model has some strengths in terms of user interface. Put another way - most calendaring applications dealing with timezones are concerned with coordinating events now and in the future - and assume further more that it is possible to present an interface which allows users to distinguish between timezones in different locales regardless of whether they might share a common abbreviation in popular usage. Then it is 'just' a matter of completeness to instantiate every timezone in use now, and to keep that current moving forward, while preserving the historical data. Then, given a localtime and a "timezone" (abstracted as a set of rules for computing offset from UTC) we can coordinate events around the globe. In fact it seems like that approach would work for historical events as well - as long as you could identify the timezone. Which is I guess the point you are making - it is much easier to go from locale to "timezone" than vice-versa, even in the present, and even if "timezone" is well defined for the user. Also I can see that you can better support a COMPLETE database with a locale based interface - the interface for exposing *every* enumerated timezone thoughout history would be overwhelming and unappreciated. tc ----- Original Message ----- From: "David Keegel" <djk(a)cyber.com.au> I think common usage outside this group is that a time zone has variable boundaries, and is something like the set of places which *currently* observe the same time (although perhaps US EST and CDT might be considered different time zones). In this model, counties in Kentucky change time zone, rather than creating a new time zone, when they switch. So translating this mindset to the computer world, if you are in Wayne County you would manually change your $TZ from US/Central to US/Eastern on 2000-10-29. Of course, this simplistic model has a fairly obvious problem. You can't compute times across a discontinuity like that in any sensible way, which is why this group has a different concept of what a time zone is - that it has a history attached and does not have variable boundaries (in theory). Might it reduce this confusion if the TZ group used something like "time zone history" or "time zone ruleset" instead of just "time zone", to distinguish it from the epheremal idea of "time zone" in popular usage? __________________________________________________________________________ David Keegel <djk(a)cyber.com.au> URL: http://www.cyber.com.au/users/djk/ Cybersource P/L: Unix Systems Administration and TCP/IP network management

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