[threeten-dev] Islamic calendar variants need disambiguation

[Dan Chiba]

Yoshito-san,

Please see my comments below:

On 12/18/2012 9:23 AM, yoshito_umaoka at us.ibm.com wrote:
> > Yoshito-san,
> >
> > I would like to get your opinion about identifying Islamic calendar
> > variants in CLDR. It defines "islamic" and "islamicc" in calendar.xml
> > for the astronomical and algorithmic variants respectively, while
> > JSR-310 needs to clearly identify the variants and distinctively
> > identify each of them, in order to identify the dates correctly.
> >
> > For example, the Umm Al-Qura calendar and Microsoft's Islamic calendar
> > implementation with the Kuwaiti algorithm are both algorithmic but they
> > are different, so the date information is not interchangeable under
> > "islamicc" between different variants. A date in one variant may
> > correspond to a different date in another variant. So, in terms of
> > ensuring correct exchange of Islamic date information, not identifying
> > the precise variants in the CLDR name space falls short of the use case
> > expectation. In JSR-310, we anticipate Islamic end users might have
> > their preferred Islamic calendar variant set in their user profile, or
> > an application may be supporting different variants in producing some
> > output with Islamic date information.
> >
> > May I ask if there is a chance to add more Islamic calendar variants or
> > enhance the calendar naming scheme to resolve this issue? Or is this
> > beyond the scope of CLDR? Do you suggest taking this to the CLDR list?
>
> I understand the issue. I don't think it's beyond the scope of CLDR.
> I think the major question is - how many variants are enough.
>
> Historically, CLDR project was spawned from ICU project. ICU calendar
> implementation is derived from a book - Caledrical Calculations
> (Nachum Deshowitz, Edward M. Reingold - ISBN 0-521-56413-1).
> In this book, "civil" calendar (arithmetic or tabular) is explained
> along with "religious" calendar which is based on astronomical
> observation. The "civil" algorithm explained in this book uses leap
> year [2,5,7,10,13,16,18,21,24,26,29] that is different from Microsoft's
> "Kawait algorithm".
>
Thank you so much for the clarifications.
> I was looking at some web pages. This page
> [http://www.staff.science.uu.nl/~gent0113/islam/islam_tabcal.htm 
> <http://www.staff.science.uu.nl/%7Egent0113/islam/islam_tabcal.htm>]
> illustrates at least four different arithmetical variations. It also
> mentions that there are two possible variations for each intercalary
> scheme based on epochs.
>
The types of variations we are aware of can be summarized as follows:
1. the different rules for tabular/arithmetic/astronomical variants
2. the different epoch used for some of the variants
3. the different deviations due to local sighting
> Also, by the nature of "religious" calendar, which may vary depending
> on astronomical observation of regional authorities, it is obviously
> not suited for identify the dates across different regions.
>
> Here is what I think -
>
> - CLDR type "islamic" is used for religious calendar now. Although
>   actual date may vary, it is probably not worth adding variations.
>
> - CLDR type "islamicc" is used for arithmetical calendar now. This
>   type could  be separated into multiple different variations.
>
> I'm wondering if you can create a CLDR ticket with proposed types?
> I can add my comment and bring this to a CLDR meeting.

Ticket #5525 opened:
http://unicode.org/cldr/trac/ticket/5525

At the moment (for JDK8), we are only interested in the Saudi Arabia 
government's official sighting and Umm Al-Qura calendar only. However, I 
think it would be adequate to make it possible to add other variants as 
needed by users or in a future release.

Regards,
-Dan

>
>
> Thanks,
> Yoshito