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RE: Year 0000

From: <zongaro@ca.ibm.com>
Date: Tue, 4 Sep 2001 10:21:33 -0400
To: "Ashok Malhotra" <ashokma@microsoft.com>
Cc: "Andrew Layman" <andrewl@microsoft.com>, lmartin@ca.ibm.com, <www-xml-schema-comments@w3.org>, <w3-xml-schema-wg@w3.org>
Message-ID: <OFE158C983.E2D87C31-ON85256ABD.0048CC27@torolab.ibm.com>
Hi Ashok,

     Sorry if my note seemed to imply that there was a discontinuity in 
the Gregorian calendar.  It certainly wasn't intended.  In particular, I 
was trying to indicate that there are no days ommitted from October, 1582 
in the proleptic Gregorian calendar; i.e., it's a month of 31 days, just 
like any other October rather than a month of 21 days.

     As for whether AD 1 is a date in the Gregorian or Julian calendar, I 
was describing common usage.  When one reads, for instance, that Miguel de 
Cervantes was born on October 9, 1547, that's a date in the Julian 
calendar; the same date in the proleptic Gregorian calendar is October 19, 
1547.  To the best of my knowledge, historians don't usually translate 
dates prior to 1582 into the Gregorian calendar, though they might need to 
for dates after 1582, prior to the Gregorian calendar's widespread 
adoption.

     Dates in the proleptic Gregorian calendar coincide with dates in the 
Julian calendar between March 1, 200 and February 28, 300.  Outside of 
that range they diverge.  The year 0000 in ISO 8601 is the year 1 BC in 
the proleptic Gregorian calendar, but it's not the 1 BC of historians or 
of common usage, which is a year in the Julian calendar.  It seemed to me 
that that was the question Andrew was asking.

     Historians using dateTime and the related data types will have to be 
aware of the difference.

Thanks,

Henry
------------------------------------------------------------------------
Henry Zongaro      XML Parsers development
IBM SWS Toronto Lab   Tie Line 778-6044;  Phone (416) 448-6044
mailto:zongaro@ca.ibm.com

Please respond to "Ashok Malhotra" <ashokma@microsoft.com> 
To:     Henry Zongaro/Toronto/IBM@IBMCA, "Andrew Layman" <andrewl@microsoft.com>
cc:     Lisa Martin/Toronto/IBM@IBMCA, <www-xml-schema-comments@w3.org>, 
<w3-xml-schema-wg@w3.org> 
Subject:        RE: Year 0000


Henry:
Your response to Andrew was not quite accurate.  ISO 8601 and XML Schema
use what is called the "prolaptic Gregorian calendar".  This means they
refer to years, months, etc as if the Gregorian calendar had been in use
since the beginning of time; specifically before 1582.  If you take this
viewpoint there is no discontinuity.
 
ISO 8601 in its usual cryptic fashion says (section 4.3.2.1 Note 2)
'Also note that the year numbers for years before the year [0001] differ
from the year numbers in the "BC/AD calendar system", where the year"1
BC" is followed by the year "1 AD"'   The Encarta article on calendars
http://encarta.msn.com/find/Concise.asp?z=1&pg=2&ti=761560321&cid=8#p8
says that "The Gregorian calendar is also called the Christian calendar
because it uses the birth of Jesus Christ as a starting date. "  So, the
BC/AD calendar, I assume from the above, uses Gregorian years.  Thus,
year [0001] corresponds to AD 1 and ... this is my interpretation ...
year [0000] corresponds to 1 BC and so on.  This is consistent if a bit
weird.
 
BTW, your notes appear in tiny font.  I assume this is some idiosyncracy
of Lotus Notes.
 
All the best, Ashok

                 -----Original Message----- 
                 From: zongaro@ca.ibm.com 
                 Sent: Mon 8/27/2001 6:25 AM 
                 To: Andrew Layman 
                 Cc: lmartin@ca.ibm.com; Ashok Malhotra;
www-xml-schema-comments@w3.org; w3-xml-schema-wg@w3.org 
                 Subject: RE: Year 0000
 
 

 
                 Hi Andrew, 
 
                      Perhaps I was a bit imprecise in saying that the 
year 0000
in ISO 8601 is what is commonly called 1 BCE.  The year 1 BCE is a year
in the Julian calendar, whereas ISO 8601 treats the Gregorian calendar
as if it existed prior to 1582-10-15, and extends it indefinitely back
in time.  So 0000 in ISO 8601 and 1 BCE overlap to a great extent, but
not necessarily completely. 
 
                      1582-10-05 is the day after 1582-10-04, and 
1582-10-14 is
the day before 1582-10-15 in ISO 8601.
 
                 Thanks,
 
                 Henry
 
------------------------------------------------------------------------
                 Henry Zongaro      XML Parsers development
                 IBM SWS Toronto Lab   Tie Line 778-6044;  Phone (416) 
448-6044
                 mailto:zongaro@ca.ibm.com
 

                 Please respond to "Andrew Layman" <andrewl@microsoft.com> 


                 To:        Lisa Martin/Toronto/IBM@IBMCA, "Ashok 
Malhotra"
<ashokma@microsoft.com> 
                 cc:        Henry Zongaro/Toronto/IBM@IBMCA,
<www-xml-schema-comments@w3.org>, <w3-xml-schema-wg@w3.org> 
                 Subject:        RE: Year 0000 
 
 
                 In that case, is 1582-10-05 a valid ISO 8601 date?  What 
day
follows
                 1582-10-04?  What day precedes 1582-10-15?  Are the 
answers to
these
                 questions consistent with the assumption that year 0000 
is 1
BCE?
 
                 -----Original Message-----
                 From: lmartin@ca.ibm.com [mailto:lmartin@ca.ibm.com] 
                 Sent: Friday, August 10, 2001 2:08 PM
                 To: Ashok Malhotra
                 Cc: zongaro@ca.ibm.com; www-xml-schema-comments@w3.org;
                 w3-xml-schema-wg@w3.org
                 Subject: RE: Year 0000
 
 
                 Yes, I'll add it to our Issues list.
                 Lisa.
 
 
                 "Ashok Malhotra" <ashokma@microsoft.com> on 08/10/2001 
04:11:14
PM
 
                 Please respond to "Ashok Malhotra" 
<ashokma@microsoft.com>
 
                 To:   Henry Zongaro/Toronto/IBM@IBMCA
                 cc:   <www-xml-schema-comments@w3.org>,
<w3-xml-schema-wg@w3.org>, Lisa
                      Martin/Toronto/IBM@IBMCA
                 Subject:  RE: Year 0000
 
 
                 Yes, I came to the same conclusion after rereading the 
2000
version of
                 ISO 8601. I think we need to consider this as a possible 
errata
item.
                 Lisa, can you please add to the errata list.
 
 
 
                 All the best, Ashok
 ===========================================================
 
                     -----Original Message-----
                     From: zongaro@ca.ibm.com [mailto:zongaro@ca.ibm.com]
                     Sent: Friday, August 10, 2001 1:01 PM
                     To: Ashok Malhotra
                     Cc: www-xml-schema-comments@w3.org; 
w3-xml-schema-wg@w3.org;
                     lmartin@ca.ibm.com
                     Subject: RE: Year 0000
 
 
 
                     Hi Ashok,
 
                          Although ISO 8601:2000 isn't entirely clear on 
the
point, it
                 does
                     say that the year numbers are contiguous.  I take 
that to
mean that
                     0000 is the year before 0001, and -0001 is the year 
before
that.
                 That
                     would mean 0000 is what is usually referred to as 1 
BC (or 1
BCE)
                 and
                     -0001 is 2 BC (or 2 BCE).
 
                          If my understanding is correct, that means the 
years
that are
                     commonly called 1BC (0000) and 5BC (-0004) are leap 
years in
the
                     proleptic Gregorian calendar, but 4BC (-0003) is not.
 
                     Thanks,
 
                     Henry
 
 
------------------------------------------------------------------------
 
                     Henry Zongaro      XML Parsers development
                     IBM SWS Toronto Lab   Tie Line 778-6044;  Phone (416)
448-6044
                     mailto:zongaro@ca.ibm.com
 
 
                     Please respond to "Ashok Malhotra" 
<ashokma@microsoft.com>
 
 
                     To:        Henry Zongaro/Toronto/IBM@IBMCA,
                     <www-xml-schema-comments@w3.org>
                     cc:        <w3-xml-schema-wg@w3.org>, Lisa
Martin/Toronto/IBM@IBMCA
                     Subject:        RE: Year 0000
 
 
                     I found additional confirmation that the 2000 version 
of ISO
8601
                     does,
                     indeed, allow the year 0000.  I don't know what it 
maps to
in terms
                 on
                     AD and BC because AD 1 == 0001 and BC 1 == -0001. 
Should we
                 discuss
                     as
                     a possible errata item.
                     Ashok
 
                                     -----Original Message-----
                                     From: zongaro@ca.ibm.com
                                     Sent: Thu 8/9/2001 2:02 PM
                                     To: www-xml-schema-comments@w3.org
                                     Cc:
                                     Subject: Year 0000
 
 
 
 
                                     Hello,
 
                                          I just saw a copy of ISO 
8601:2000.  I
was
                     surprised to
                     discover that it defines 0000 to be a valid year, 
unlike the
                     specification of dateTime in the "XML Schema: 
Datatypes"
                     recommendation
                     [1].  I gather that in ISO 8601:2000, the year 0000 
is
roughly 
                      equivalent to what people usually refer to as 1BC, 
and is a
leap
                 year.
 
                                          Should dateTime follow ISO 
8601:2000 in
this
                     respect?
 
                                     Thanks,
 
                                     Henry
                                     [1]
                     http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/#dateTime
 
 
 
------------------------------------------------------------------------
 
                                     Henry Zongaro      XML Parsers 
development
                                     IBM SWS Toronto Lab   Tie Line 
778-6044;
Phone
                 (416)
                     448-6044
                                     mailto:zongaro@ca.ibm.com
 
 
 
 
 
 
 
Received on Tuesday, 4 September 2001 10:21:36 GMT

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