semantic web request result difference - sparql

Question

PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT * WHERE {
?x foaf:primaryTopic ?n .
?x rdf:type ?z .
FILTER (regex(?x, '^http://en.wikipedia.org/wiki/Barack_Obama$')).
}
LIMIT 10
when i call this request from http://dbpedia.org/snorql, it works. but when i try below
SELECT * WHERE {
?x foaf:primaryTopic ?n .
?x rdf:type ?z .
?x owl:activeYearsStartDate ?v .
FILTER (regex(?x, '^http://en.wikipedia.org/wiki/Barack_Obama$')).
}
it doesn't work. but why?

Answer 1

I expect that you meant
?x dbpedia-owl:activeYearsStartDate ?v .
rather than
?x owl:activeYearsStartDate ?v .
Also, using regex here is more expensive than it needs to be. You could check whether the string value of a URI is something in particular with
filter( str(?x) = "…" )
but even that is a lot more work than you need. If you want ?x to be <http://en.wikipedia.org/wiki/Barack_Obama>, just use it instead of ?x, or bind ?x to it with values:
SELECT * WHERE {
<http://en.wikipedia.org/wiki/Barack_Obama> foaf:primaryTopic ?n .
<http://en.wikipedia.org/wiki/Barack_Obama> rdf:type ?z .
<http://en.wikipedia.org/wiki/Barack_Obama> owl:activeYearsStartDate ?v .
}
SELECT * WHERE {
values ?x { <http://en.wikipedia.org/wiki/Barack_Obama> }
?x foaf:primaryTopic ?n .
?x rdf:type ?z .
?x owl:activeYearsStartDate ?v .
}
That still looks suspicious, though. Are you sure you didn't want <http://dbpedia.org/resource/Barack_Obama>? And the use of foaf:primaryTopic stuff really makes me think that you want something more like:
select * {
?x foaf:isPrimaryTopicOf <http://en.wikipedia.org/wiki/Barack_Obama> ;
a ?type ;
dbpedia-owl:activeYearsStartDate ?v
}
limit 10
SPARQL results