How to extract data from DBpedia using SPARQL - sparql

Question

I'm trying to extract some data from dbpedia using SERVICE function of SPARQL.
In fact I want to extract the names, the lat and lot of all New York theaters. To check if an instance is a theater I can use http://dbpedia.org/class/yago/Theater104417809​. One example of a theater could be http://dbpedia.org/resource/Grand_Theatre_(New_York_City).
How to use service function for getting what I need in SPARQL?
** EDIT **
The query that I'm trying is the following one, but is not returning any value.
PREFIX dbpedia: <http://dbpedia.org/ontology/>
PREFIX dbp: <http://dbpedia.org/property/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX geos: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
PREFIX : <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#>
SELECT *
WHERE {
SERVICE <http://dbpedia.org/sparql/> {
SELECT ?teatreName ?lat ?long
WHERE {
?teatre rdf:type dbpedia:Theatre .
?teatre foaf:name ?teatreName .
?teatre geo:lat ?lat .
?teatre geo:long ?long .
?teatre dbp:city ?ciutat .
?ciutat rdfs:label "New York City"#en
}
}
}

Answer 1

It's not an issue with federated querying, but with your DBpedia query. dbp:city is not an object property but simply of type rdf:Property, thus it's untyped. In your case, it maps to literals which means, you have to use the literal directly. The weird thing here is, that for some reasons you have to use the datatype http://www.w3.org/1999/02/22-rdf-syntax-ns#langString explicitly instead of "New York City"#en - that's clearly not intuitive for any user. Not sure whether this happened due to the DBpedia extraction or is the expected behaviour of Virtuoso.
PREFIX dbpedia: <http://dbpedia.org/ontology/>
PREFIX dbp: <http://dbpedia.org/property/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX geos: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
PREFIX : <http://www.semanticweb.org/frubi/ontologies/2017/10/puntsWIFI#>
SELECT *
WHERE {
SERVICE <http://dbpedia.org/sparql/> {
SELECT ?teatreName ?lat ?long
WHERE {
?teatre rdf:type dbpedia:Theatre .
?teatre foaf:name ?teatreName .
?teatre geo:lat ?lat .
?teatre geo:long ?long .
?teatre dbp:city "New York City"^^<http://www.w3.org/1999/02/22-rdf-syntax-ns#langString>
}
}
}