Omission in the recommendation SPARQL 1.1 and in the tests : the operators with datetime

[BorderCloud]

As Sebastian Schaffert said:

Date subtraction not defined by SPARQL 1.1
The test for date subtraction in test Grid Observatory does not conform to the SPARQL 1.1 specification.
The operator "-" is only defined for numeric operands.
http://www.w3.org/TR/sparql11-query/#OperatorMapping

In the recommendation, we can read "The following table associates each of these grammatical productions with the appropriate operands and an operator function defined by either XQuery 1.0 and XPath 2.0 Functions and Operators [FUNCOP] or the SPARQL operators specified in section 17.4.".
In the "operator function defined by either XQuery 1.0 and XPath 2.0", we can see "Backs up the subtract, "-", operator on xs:dateTime values"

Proposition of new test for the substract's operator with datetime :

PREFIX xsd:<http://www.w3.org/2001/XMLSchema#>
SELECT   ?date1 ?date2 ( ?date1-?date2 AS ?funcSubtractDateTimes) 
{ 
    BIND (xsd:dateTime("2005-01-02T00:00:01Z") AS ?date1)
    BIND (xsd:dateTime("2005-01-01T00:00:00Z") AS ?date2)
}

Result expected :

----------------------------------------------------------------------------------------------------------------
| date1                                | date2                                | funcSubtractDateTimes          |
================================================================================================================
| "2005-01-02T00:00:01Z"^^xsd:dateTime | "2005-01-01T00:00:00Z"^^xsd:dateTime | "P1DT0H0M1.000S"^^xsd:dayTimeDuration |
----------------------------------------------------------------------------------------------------------------

What did you think ?

[VladimirAlexiev]

The row defining - (minus) explicitly says "numeric" and links to https://www.w3.org/TR/xpath-functions/#func-numeric-subtract. So indeed, SPARQL doesn't define subtraction of dates.

Date subtraction is a reasonable extension, but you should somehow mark it as an extension.
Also, you should write 1S instead of 1.000S, #15 raises a similar problem.