Federated queries on dbpedia and linkedmdb - sparql

Question

I am writing a federated query to get the books based on films in dbpedia and in turn using the film name from dbpedia to retrieve the corresponding imdblink link for the same. I am getting an empty set when I add the service of linkedmdb.
Here is my code
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX dc: <http://purl.org/dc/terms/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dbp: <http://dbpedia.org/property/>
SELECT distinct ?name ?author ?filmname ?imdbID WHERE {
SERVICE <http://dbpedia.org/sparql> {
?book rdf:type dbo:Book .
?book foaf:name ?name .
?book dbp:author ?author .
?author foaf:name ?authname .
?book ^dbo:basedOn ?movie .
?movie a dbo:Film .
?movie foaf:name ?filmname
FILTER (str(?name) IN ("Royal Flash","White Oleander", "Possession: A Romance", "Misery", "Intensity", "The War of The Roses", "Momo", "The Sicilian", "Derailed", "Ragtime"))
}
SERVICE <http://data.linkedmdb.org/sparql> {
?filmname foaf:page ?imdbID .
?filmname dc:title ?title .
FILTER(regex(str(?imdbID), "www.imdb.com" ) )
}
}
I am using the following endpoint http://www.sparql.org/query.html

Answer 1

That does not work because of the ?filename variable
in the first SERVICE clause you get
?movie foaf:name ?filmname, thus, those are string literals
in the second SERVICE clause ?filmname are URIs
It will become easy to see if you run both SPARQL queries separately.
What you would have to do is to match on the title, i.e. change
?filmname dc:title ?title .
to
?filmname dc:title ?filmname .
Note, this might not work because of different types of strings, e.g. with and without language tag etc.
In that case you would have to match on the lexical form again, i.e. use temporary variables ?filmname1 and ?filmname2 and use
FILTER(str(?filmname1) = str(?filmname2))
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbp: <http://dbpedia.org/property/>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc: <http://purl.org/dc/terms/>
SELECT DISTINCT ?name ?author ?filmname1 ?imdbID
WHERE
{ SERVICE <http://dbpedia.org/sparql>
{ ?book rdf:type dbo:Book ;
foaf:name ?name ;
dbp:author ?author .
?author foaf:name ?authname .
?book ^dbo:basedOn ?movie .
?movie rdf:type dbo:Film ;
foaf:name ?filmname1
FILTER ( str(?name) IN ("Royal Flash", "White Oleander", "Possession: A Romance", "Misery", "Intensity", "The War of The Roses", "Momo", "The Sicilian", "Derailed", "Ragtime") )
}
SERVICE <http://data.linkedmdb.org/sparql>
{ ?filmname foaf:page ?imdbID ;
dc:title ?filmname2
FILTER regex(str(?imdbID), "www.imdb.com")
}
FILTER ( str(?filmname1) = str(?filmname2) )
}