I've corrected this. The note now reads:
Years with more than four digits are valid if approved by profile. The
profile (for example, this specification) must specify the number of digits
and then all extended years must use that number of digits. An extended year
then is any year with greater than four digits, or any year earlier than
For example suppose this specification says that extended years are six
Any year between 0000 and 9999 is represented with four digits.
Any year later than 9999 is represented with six digits whether it needs
them or not, thus the year 10000 is represented as '010000'.
Any negative date is represented with six digits, whether it needs them or
not. Thus the year -10000 is represented
The year zero is represented as '0000'.
( Note that 0000 has the same meaning as 1 BC. There is no zero BC.)
From: Discussion of the Developing Date/Time Standards
[mailto:[log in to unmask]] On Behalf Of ashtongj
Sent: Thursday, August 05, 2010 7:24 PM
To: [log in to unmask]
Subject: Re: [DATETIME] EDTF Features list
My (electronic) copy of ISO 8601:2004 says (the html tags are added by me to
expansion of a representation to allow identification of dates in
calendar years outside the range  till 
The introduction to the standard explains that square brackets are to
distinguish date/time representations from the text of the standard, and the
square brackets are not part of the representation. Since 0000 is withing
the range 0000 till 9999, I would use four digits for the year zero, not 6.
Also, I am at a loss to understand why you would want to use a negative sign
with the year zero.
The text provides further support for this interpretation in section 3.2.1,
The Gregorian Calendar. It states:
NOTE In the proleptic Gregorian calendar, the calendar year
 is a leap year.
On 2010-08-05 6:59 PM, Ray Denenberg wrote:
> " Please see page 7 of ISO 8601:2004."
> I don't think our copies are paged alike, could you cite by section
> instead of page?
> Anyway, I think it should have said "The year zero is represented as
> '-000000'." rather than "The year zero is represented as '-000001'."
> And 1 BC would be the same as year zero thus '-000000'. Right?
> -----Original Message-----
> From: Discussion of the Developing Date/Time Standards
> [mailto:[log in to unmask]] On Behalf Of ashtongj
> Sent: Thursday, August 05, 2010 6:43 PM
> To: [log in to unmask]
> Subject: Re: [DATETIME] EDTF Features list
> I believe the consolidated table contains an error. Section 2
> subsection "Extension and Precision" rightmost column last bullet says
> "The year zero is represented as '-000001'." But of course the
> notation other than AD/BC or CE/BCE that is most widely known is
> astronomical year numbering, in which the year 0 would be represented
> as 0000 in ISO 8601 notation. It is the year
> 1 BC that would be represented as '-000001'
> when a profile had been agreed to that required six digits for
> expanded year representation.
> Please see page 7 of ISO 8601:2004.
> Gerard Ashton