W3C home > Mailing lists > Public > xmlschema-dev@w3.org > July 2001

Re: Date

From: <Noah_Mendelsohn@lotus.com>
Date: Thu, 5 Jul 2001 12:03:36 -0400
To: "Jeff Rafter" <jeffrafter@definedweb.com>
Cc: vdv@dyomedea.com, xmlschema-dev@w3.org
Message-ID: <OFFE14C507.8F3692AA-ON85256A80.00576518@lotus.com>
Jeff Rafter writes:

>> does this mean that an optional Time Zone Qualifier 
>> should be added

Not sure, but there is some background that may be of interest.  First, 
many readers fail to recognize that in XML Schema Datatypes, timezone 
indicators are in the lexical representations only.  Their status is 
similar to leading zeros, or exponential notations (1E+2)  vs. 
unnormalized floats (100.0); timezones are visible, but not considered to 
affect the value of the time or integer respectively.  The times 
themselves are all effectively converted to a fixed UTC form for 
comparison or other use as values.  This also has the interesting effect 
that two different times in different timezones can be considered equal 
for purposes of enumeration, as are the two floats above.  I argued 
against this design for timezones in particular, as I think it violates 
least-astonishment for users, but there it is.  I believe that users 
consider timezones more significant than leading zeros.   No matter, that 
is the starting point for any future evolution.  I would have preferred to 
allow no timezone at all than one that has such minimal effect on 
semantics and comparison.

Also, Lotus (my employer) has some experience building timezone-aware 
applications.   Turns out we have had bugs reported, in calendaring 
applications for example, that were caused by political rather than 
technical actions.   A user schedules a meeting at 3PM in GMT-6, but they 
really think they're scheduling it in Chicago.  Chicago changes its laws, 
and the calander rings the alarm too early or late...it is indeed GMT-6, 
but it's no longer 3PM in Chicago.  These are real bugs from real users. 
Some people argued for making the timezone dependent on an online 
catalog...I think many of us feel that has a variety of undesireable 
characteristics.  On the other hand, this should be taken as a warning 
that solving users' problems with timezones is not nearly as easy as it 
appears, and sometimes it is better to do less than to add complexity that 
doesn't solve the problem.  For better or worse, schemas effectively 
provides timezone markers primarily as a convenience to those recording 
times in an XML document;  it carries little or no semantics compared to 
the same time in UTC.

Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Received on Thursday, 5 July 2001 12:09:07 UTC

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