Getting time interval - sparql

Question

Apologies if this has been asked before but it seems an obvious question for which I can't seem to get a working solution. I've loaded some data into Fuseki which contains statements comprising xsd:date information. I have written a query to extract these dates and I would like to find the duration (in days) between two specific date. A cut down query is shown below.
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX abc: <http://www.acme.com/ABC/1.0/abc-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
SELECT ?entry
(date1 - date2) AS ?interval)
WHERE
{
# Not the real query but you get the idea
?entry a abc:thing ;
abc:abcDateType1 ?date1 ;
abc:abcDateType2 ?date2 .
}
?interval is calculated correctly and seems to be in the form of an xsd:duration data type, my question is how do I extract the number of days it contains? Alternatively is there a better (standard) way of doing this.
Thank you for reading.

Answer 1

You will need to work with the lexical for of the XSD duration. It is likely to be for the form "PD...."
The answer should be call fn:days-from-duration, or a keyword for that function, but that isn't in the standard distribution at the moment.

Answer 2

One way would be to add unix-style timestamps related to a date, abstractly:
?blankNode eg:hasDate ?date
?blankNode eg:hasEpoch ?epoch
Then you can easily subtract the timestamp for one day from the other, and divide by 86400 to give the answer in day, e.g.:
SELECT ?entry
((?time1 - ?time2)/86400) AS ?interval)
WHERE
{
# Not the real query but you get the idea
?entry a abc:thing ;
abc:abcDateType1 ?date1 ;
abc:abcDateType2 ?date2 .
?blankNode1 hasDate ?date1 .
?blankNode1 hasTime ?time1 .
?blankNode2 hasDate ?date1 .
?blankNode2 hasTime ?time1 .
}