[d2rq-dev] Calculating dateTime differences in D2RQ

[Kārlis Č. <kar...@lu...>]

Dear D2RQ creators and users,

is there any way, how to calculate a difference (in days) between two 
datetime (or date) values over D2RQ SPARQL endpoint?

I am trying something like (on D2RQ master branch snapshot 0.8.2.-dev):

SELECT DISTINCT ?n ?p ?c ?d WHERE {
   ?s a ont:Student.
   ?s ont:personName ?n.
   ?r a ont:Registration.
   ?r ont:datePaid ?p.
   ?r ont:dateCompleted ?c.
   BIND ( ?c - ?p AS ?d).
}

This is OK with parsing, however, I get empty results for ?d:

n	p	c	d
"Dave"^^xsd:string	"2013-01-10T00:00:00"^^xsd:dateTime 
"2013-06-22T00:00:00"^^xsd:dateTime	-
"Eve"^^xsd:string	"2013-01-10T00:00:00"^^xsd:dateTime 
"2013-06-22T00:00:00"^^xsd:dateTime	-
"Charlie"^^xsd:string	"2013-01-10T00:00:00"^^xsd:dateTime 
"2013-06-22T00:00:00"^^xsd:dateTime	-
"Ivan"^^xsd:string	"2013-01-10T00:00:00"^^xsd:dateTime 
"2013-06-22T00:00:00"^^xsd:dateTime	-

It would be easy to calculate "approximate" duration values, using YEAR, 
MONTH and DATE functions; the question is, if the actual date difference 
can be computed.

Thanks,
Karlis Cerans