1226Re: [ISO8601] Re: meaning of time-interval
- Feb 1, 2005If someone was born on 2004-02-29 when is their first birthday? You
might say 2005-03-01 or 2005-02-28. Does that mean that they have the
same birthday as someone born on 2004-03-01 or 2004-02-28?
There is a general expectation of addition that subtraction of the
addend from the sum gives the original.
Arbitrary arithmetic is not be possible using any units. You cannot
add anything to 1997-06-30T23:59:60Z except for 1Y6M and similar. A
small number of seconds would be okay but a large interval could not
extend more than a few months into the future because of
unpredictability of leap seconds. Any other units would produce a
result with 60 in the seconds.
The only way to do correct interval arithmetic is to use something
like TAI. But that is off topic for ISO 8601.
IMHO the intent of time-intervals involving duration in ISO 8601 is
that the start + duration or end - duration should (must?) be a valid
date-time without having to apply any normalization rules.
Pete Forman -./\.- Disclaimer: This post is originated
WesternGeco -./\.- by myself and does not represent
pete.forman@... -./\.- opinion of Schlumberger, Baker
http://petef.port5.com -./\.- Hughes or their divisions.
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