Re: date arithmetic

David Sinclair asked:

I want to add 6 months to a date (in xslt2.0) but cant find any
references on how to do this. After much googling I tried something like:

<xsl:value-of select="xs:date($reviewDate) + xs:duration('P0Y0M6DT0H00M')"/>
But the processor (Saxon 8.0) says that date arithmetic is not supported on xs:duration. If I am barking up the right tree, then what are the supported subtypes? Hope someone can help,

Mike Kay replied:

xs:date($reviewDate) + xdt:yearMonthDuration('P6M')

Just to flesh out Mike's reply a bit...

xs:duration is defined by XML Schema as a number of years, months,
days, hours, minutes and seconds. The trouble is that it's not
possible to give definitive answers to comparisons when you have
durations that contain both years or months and days, hours, minutes
or seconds. For example, which is longer, one month or 30 days? In
technical terms, xs:duration is "partially ordered".

XPath 2.0 dodges the question by only supporting two "totally ordered"
subtypes of xs:duration: durations that only involve years and months
(xdt:yearMonthDuration) and durations that only involve days, hours,
minutes and seconds (xdt:dayTimeDuration).

If you want to add a duration that combines the two subtypes, you need
to add one and then the other, as in:

 (current-date() + xdt:yearMonthDuration('P1Y')) +
 xdt:dayTimeDuration('P1D')

(Of course, the order in which you add them makes a difference to the
result...)

Note that you don't have to include a component if there are 0 of
them: if you have 0 days in a duration, you don't need to put '0D' in
it.

Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/