[tz] OpenJDK/CLDR/ICU/Joda issues with Ireland change

Yoshito Umaoka yoshito_umaoka at us.ibm.com
Thu Jan 25 02:48:25 UTC 2018

> > CLDR sets an assumption that name of zones are very stable. For 
> > "Pacific Standard Time" represents standard time used on US Pacific 
> > and the name itself does not change time to time.
> Could you clarify how CLDR currently works for Ireland, without the 
> proposed tzdb changes? tzdb's current data (which is the same as what it 

> was in 2017c) has three types of Irish timestamps that use the 
> abbreviation "IST". The first type is for UT+00:34:39 and was observed 
> in summer 1916; it has tm_isdst=1. The second type is for UT+01 and was 
> observed in summers from 1922 through late 1940, then continuously until 

> late 1948, then in summers through 1968, and then in summers from 1972 
> through today; it also has tm_isdst=1. The third kind is also for UT+01 
> and was observed from late 1968 through late 1971; it has tm_isdst=0.
> Are all three types of IST called "Irish Standard Time" in CLDR now? If 
> not, then what does CLDR call them and how is this determined? And if 
> so, we have a problem since the correct full name for IST is "Irish 
> Summer Time" for timestamps before late 1968, and is "Irish Standard 
> Time" for timestamps thereafter, and there's nothing in the tzdb data 
> proper that specifies the transition date between the two full names.

CLDR does not have time zone names for dates before 1990. Historic
zone names never used in a last few decades are not included. This is 
because reducing overhead of managing localized names. Our primary focus
is to provide good localized display names in modern software, not trying
to provide every possible names historically used.

CLDR suggests code implementators to use a UTC offset format as the 
for example, UTC+01:00 as the fallback when a name is not available.
(CLDR also provides localized fallback format patterns in various 

BTW, CLDR localized names are also based on ordinary people's expectation
in each locale. For example, while people in Ireland most likely recognize
"IST" as "Irish Standard Time", but people in other countries usually do
not recognize what "IST" is. In CLDR, these zone abbreviations are managed
as "short" names, and the coverage of short names is sparse in each 
In this example, locale en-US does not have short name for Irish Standard
Time. "IST" is used as the short name only in locale en-IE (IE = Ireland).
Again, when a zone name is missing, CLDR suggests code implementators to
use the fallback format.

> CLDR is not cast in stone: CLDR called IST "Irish Summer Time" until 
> CLDR 26 came out in 2014 - this fixed a bug with post-1968 timestamps at 

> the cost of introducing a bug for pre-1968 timestamps. I'm hoping that 
> there is some way that we can fix this problem, a problem that exists 
> regardless of whether negative DST offsets are used. Perhaps CLDR could 
> be extended somehow, so that its reports the proper full names for time 
> zones even if that info is not always deducible from the tzdb data 

So, the issue between Irish Summer Time and Irish Standard Time is
irrelevant to CLDR with our current scope.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mm.icann.org/pipermail/tz/attachments/20180124/c77e1ecd/attachment.html>

More information about the tz mailing list