Hi Harri,
https://www.w3.org/TR/xpath-functions-3/#func-subtract-dates
The difference of two dates is the duration bwteeen the dates as points
on the timeline as a xs:dayTimeDuration.
?age is "P14484DT0H0M0.000S"^^xsd:dayTimeDuration
not PnnYnnMnnD
A duration is a defined, fixed length of time.
There two kinds of durations xs:dayTimeDuration and xs:yearMonthDuration
https://www.w3.org/TR/xpath-functions-3/#duration-subtypes
where arithmetic and ordering can be meaningfully defined at all.
A combination of months and days is not a fixed interval of time because
the number of days in a month isn't the same for all months.
Only xs:dayTimeDuration defines a duration that is of a well-defined
difference of two points on the timeline (ignoring negative leap seconds).
Once "xsd:date - xsd:date" is calculated, the duration is a fixed length
of time and does not tie back to which dates were used in the calculation.
So "P14484D.." is right not "P44Y6m??D"
[[
Confusingly the difference of two Gregorian year-months (gYearMonth) is
also an xs:dayTimeDuration, and not a xs:yearMonthDuration, not that it
is really defined on gYearMonth (section 9.1), because gYearMonth maps
to a point on the timeline and the difference is of two points on the
timeline.
]]
With ?age is "P14484DT0H0M0.000S"^^xsd:dayTimeDuration
For the casting to xsd:yearMonthDuration: (had to check this one!)
Casting xsd:dayTimeDuration to xsd:yearMonthDuration is defined.
https://www.w3.org/TR/xpath-functions-31/#casting-from-primitive-to-primitive
https://www.w3.org/TR/xpath-functions-31/#casting-to-durations
"""
If ST is xs:yearMonthDuration and TT is xs:dayTimeDuration, the cast is
permitted and returns a xs:dayTimeDuration with value 0.0 seconds.
"""
ST is "source type" TT is target type".
I don't know the rationale - (a guess - treat like it is selecting
fields from PnnYnnMnnDT..)
Andy
On 27/01/2021 17:16, Harri Kiiskinen wrote:
Dear all,
This example run with Fuseki 3.17:
--------------------------------------------------------------------
PREFIX fn: <http://www.w3.org/2005/xpath-functions#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?y ?d (xsd:dayTimeDuration(?age) as ?a1)
(xsd:yearMonthDuration(?age) as ?a2)
where {
bind ( xsd:date("1984-12-01") as ?y)
bind ( xsd:date("1944-05-06") as ?d)
bind ((?y-?d) as ?age )
}
-------------------------------------------------------------------
Gives unexpected results:
------------------------------------------------------------------
y,d,a1,a2
1984-12-01,1944-05-06,P14484DT0H0M0.000S,P0M
------------------------------------------------------------------
I was expecting the variable "a2" to contain the duration expressed in
Years and Months, but instead it is zero.
What am I doing wrong here?
Best,
Harri Kiiskinen
