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Thanks for the comments, Gerry. I've split off the UTC issue to a different 
thread and focus on BC here.

It looks to me like the W3C does not currently treat BC dates as you 
suggest, but that they are thinking of changing this in the next version.
 In other words,  "-1000" means "1000 BC" and there is no year zero, 
according to the current spec. But that same current spec notes that they 
have been lobbied to change it as you suggest, that 1000 BC would be -999. 
So at this point, it seems that we need to try to determine their 
intentions.

--Ray

----- Original Message ----- 
From: Gerry Ashton
To: [log in to unmask]
Sent: Monday, November 30, 2009 5:59 PM
Subject: [DATETIME] BC, UTC



The requirements page states "BC dates. For example '-1000' for 'the year 
1000 BC'".
But of course the year 1000 BC is also the year -999. Too many people are 
familiar
with this usage, and are familiar with the basic methods of performing 
arithmetic
with negative numbers, to dissassociate the symbol "-" with its meaning as a
negative sign and reassign it as a synonym for BC.

The requirements page also uses the term UTC. However, depending on how you
want to look at it, UTC did not come into existence until sometime between 
1961
and 1972. Its properties were quite different from what we are used to until 
1972.
Thus, it might be best to adopt various time definitions, such as "time is 
expressed
in UT before 1 January 00:00 UTC and in UTC thereafter." Or perhaps be 
agnostic:
"time is expressed in UT, but the precise variety of UT used is outside the 
scope
of this standard."

Gerry Ashton