At 2012-09-17 20:01 +0000, Costello, Roger L. wrote:
Hi Folks,
Why does this expression return true:
xs:date('2012-09-10+14:00') lt xs:date('2012-09-11-14:00')
September 10, 2012 plus 14 hours is less than September 11, 2012
minus 14 hours?
As I calculate it,
September 10, 2012 plus 14 hours is 2:00 PM on September 10, 2012
and
September 11, 2012 minus 14 hours is 10:00 AM on September 10, 2012
No?
No, not at all. Your mistake is that it isn't a calculation.
The +14:00 is not a time delta, it is an indication of where in the
world the date you have is found. And I'm not sure +/- 14:00 is
allowed ... I think time zones only go up to +/-13:00. Ah, I'm
wrong, there is a +14:00, and there is a -12:00, but nothing beyond:
http://en.wikipedia.org/wiki/UTC%2B14:00
http://en.wikipedia.org/wiki/UTC-12:00
Let's take an easier example, with two valid time zones:
2012-09-11-04:00 is September 11, 2012 in the Eastern Time Zone
2012-09-10+04:00 is September 10, 2012 in the Persian Gulf
September 10, 2012 is still before September 11, 2012
We are still only talking about dates ... you do not have any time
component, you only have the time-zone component.
And even adding a time component, let's look at noon in both time zones:
2012-09-10T12:00+04:00 is 32 hours before 2012-09-11T12:00-04:00.
Because when you normalize the time zone to a common time zone:
2012-09-10T12:00+04:00 is 2012-09-10T08:00UTC
2012-09-11T12:00-04:00 is 2012-09-11T16:00UTC
... which are 32 hours apart
So, the "+/1XX:YY" is only a time zone indicator, not an operand in
any arithmetic when comparing dates. It becomes an operand when
adjusting the date or time or dateTime value to UTC.
I hope this helps.
. . . . . . . . . Ken
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