Bob MacGregor wrote:
Hi Lee,
OK, we'll try sparql dev, as long as this is a how to, rather than a
"can't be
done". But it looks to me like
your query returns no bindings if an article does not have a timetag. I
say this because of the {?a ex:timetag ?maxtime} clause
that comes before the OPTIONAL. But in that case, it should return
the article. Can you fix this, or is it not expressible after all?
Right, I did that purposefully to concentrate on the "max" idiom. If you
want to include articles with no timetag, it becomes:
PREFIX : <http://example.org/>
SELECT ?a
FROM <http://thefigtrees.net/lee/sw/data/times.ttl>
WHERE {
?a a :article .
OPTIONAL {
?a :timetag ?maxtime .
OPTIONAL {
?a :timetag ?othertime . FILTER(?othertime > ?maxtime)
}
FILTER (!bound(?othertime))
}
FILTER(!bound(?maxtime) || ?maxtime < 5)
}
The key is, I guess, to make the whole "find the max time" part optional
and then filter outside that on "there is no maxtime or the maxtime is
early enough".
(Note, I put some actual data at the above URL so that you can try this
out. To do this I changed the predicate names a bit and used integers
instead of datetimes for simplicity. I made "now" equal to 5. :-) ARQ
deployed at http://sparql.org is a great place to try it.)
The data is:
@prefix : <http://example.org/> .
:onetimeOK a :article ; :timetag 1 .
:onetimeNotOK a :article ; :timetag 10 .
:twotimesOK a :article ; :timetag 1, 2 .
:twotimesNotOK a :article ; :timetag 1, 10 .
:notimeOK a :article .
... and when I run the above query through ARQ at sparql.org I get:
a:
<http://example.org/notimeOK>
<http://example.org/twotimesOK>
<http://example.org/onetimeOK>
Lee
In SPARQL, this query is (unedited, untested):
SELECT ?a
FROM :model
WHERE {
?a rdf:type ft:article ; ex:timetag ?maxtime .
OPTIONAL { ?a ex:timetag ?othertime . FILTER(?othertime > ?maxtime) }
FILTER (!bound(?othertime) && ?maxtime > '...now...')
}
Original target:
SELECT ?a
FROM model
WHERE
(?a rdf:type ft:Article) AND
UNSAID ((?a ex:timetag ?time) AND
(?time > $NOW))
=====================================
Robert MacGregor
Chief Scientist
Siderean Software, Inc.
[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
Mobile: 310-469-2810
=====================================
