Hello,
I am trying to retrieve a list of predicates from DBpedia with a SPARQL query.
The full set looks fine:
SELECT DISTINCT ?b
WHERE {
?a ?b ?c.
}
LIMIT 50
On http://dbpedia.org/sparql, this returns 50 URIs (let's call this set A), so
there are 50 (or probably more) predicates available.
Now, I just want a subset of this, namely only predicates whose last part in
the URI starts with a letter from A to Z:
SELECT DISTINCT ?b
WHERE {
?a ?b ?c.
FILTER(regex(str(?b), "[/#][a-z][^/#]*$", "i")).
}
LIMIT 50
This returns a surprisingly small set (let's call this set B) consisting of
only one URI (http://www.w3.org/1999/02/22-rdf-syntax-ns#type), which had also
been in set A. But if that set is so small, the complementary set should
contain at least the 49 items from set (A - B):
SELECT DISTINCT ?b
WHERE {
?a ?b ?c.
FILTER(regex(str(?b), "[/#][^a-z/#][^/#]*$", "i")).
}
LIMIT 50
I would expect the result set of this query to contain, for example,
http://www.w3.org/2002/07/owl#sameAs, which was contained in set A. Instead,
the result set of this last query (set C) is empty.
Why does DBpedia behave like that; is there anything wrong about my queries or
my regular expressions? (When trying this on some other endpoints
(http://vocabulary.semantic-web.at/PoolParty/sparql/AustrianSkiTeam ,
http://spatial.ucd.ie/lod/sparql ), the result seems to be as expected.) Note
that DBpedia's SPARQL web-frontend does not report any syntax errors, server
errors or timeouts.
Thanks in advance
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