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RE: dateTime etc accessors now UTC-based, were local

From: Kay, Michael <Michael.Kay@softwareag.com>
Date: Thu, 8 May 2003 16:26:03 +0200
Message-ID: <DFF2AC9E3583D511A21F0008C7E62106073DCDFC@daemsg02.software-ag.de>
To: David Holmes <dholmes@tibco.com>, "'public-qt-comments@w3.org'" <public-qt-comments@w3.org>

> I noticed that the Last Call (02 May 2003) Functions and 
> Operators working draft has changed from the 15 November 2002 
> draft in regards to the basis for component accessors 
> functions for dateTime and friends.
> 
> For example, where previously (Section 8.4.10.1, 15 November 2002)
> 
> fn:get-hours-from-dateTime(xs:dateTime("1999-05-31T13:20:00-05
> :00")) returns 13,
> 
> now (Section 9.4.10.1, 02 May 2003)
> 
> fn:get-hours-from-dateTime(xs:dateTime("1999-12-31T21:20:00-05
> :00")) returns 2.
> 
> It would appear that the basis for component accessors has 
> gone from local (same as lexical) to UTC.

Actually, the November draft was confused on the subject. The value space
for dates and times, as defined in XML Schema, does not retain the timezone,
so the result shown in the example was not achievable without some special
magic.

> I can understand 
> that the distinction is necessary to get everything to work 
> out right, but the user is now left with the onerous task of 
> calculating local components and surprising results unless 
> this behavior is made very explicit in the specs.

Timezones, I'm afraid, are always going to generate surprises, whatever we
do.

To get the hours component in the original timezone, I believe that what you
have to do is:

get-hours-from-dateTime(adjust-dateTime-to-timezone($dt, ()))

This might not be very intuitive, but it's not very onerous once you know
what you're doing.
> 
> Would you be able to point me to some threads on the subject? 
> Did the committee consider some parallel functions e.g. 
> get-local-hours-from- and get-utc-hours-from-?
> 

More possibilities were considered than some of us care to remember...

Michael Kay
Received on Thursday, 8 May 2003 10:26:27 GMT

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