[DFDL-WG] date & time and latest ICU possible issues/conflicts

[Steve Hanson]

ICU ticket raised as the help does not give an example.

https://icu.sanjose.ibm.com/gcoctrac/ticket/469#ticket

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     dfdl-wg at ogf.org, 
Date:   16/01/2013 15:11
Subject:        [DFDL-WG] date & time and latest ICU possible 
issues/conflicts
Sent by:        dfdl-wg-bounces at ogf.org




Steve Lawrence is on the Daffodil Open Source DFDL team (on CC), and he 
has dug into date/time types.

He raised some concerns to me that I really haven't been tracking at all, 
so I wanted to put in front of the rest of the group.

The date time format syntax for the latest version of icu4j contains a 'U' 

character, which means "cyclic year name". However, the daffodil 
spec says the 'U' character, following a Z makes it so a timezone of UTC 
is represented as Z instead of +00:00.

This seems to be a conflict, and would prevent us from ever upgrading to 
the newest version of ICU (which might be a good idea).

I will point out that the latest version of ICU supports ZZZZZ (5 Z's), 
which is the ISO8601 timezone format. This doesn't add all the 
functionality that the DFDL 'U' gives. My question is, is this enough? 
Are there cases where the ZU, ZZU, etc. are necessary? I'm just 
concerned that the U is going to quite a bit more complexity, and want 
to make sure the updates to latest ICU don't address the DFDL-WG concerns.

And if we still need the 'U', maybe it should change to a different 
letter to prevent conflicts with the latest ICU4J?

I would point out that the ICU pattern language cannot deal with 
dual-purpose letters very well, i.e., ambiguities are introduced if the 
same letter both introduces a format, and if following another format 
string, modifies its behavior. E.g., does ZU mean Z modified by U, or Z 
first, and then U. So it seems pretty unfortunate if the ICU libraries 
added a conflicting use of letter U.

I believe the point of DFDL's use of the U modifier for letters I and Z 
was to be absolutely clear on the GMT timezone 'Z' issue, i.e., to 
indicate that 'Z' is to be used, and -00:00 is not to be output, nor 
accepted when parsing. The ICU specification ZZZZZ says ISO format, but 
that allows either 'Z' or -00:00 to be used for GMT timezone, and it's not 
clear what it means on output. 

-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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