SPARQL get dbpedia ressources by category - sparql

Question

I'm a beginner in SPARQL. And I'm having problems to get the latitude and longitude of all university by city on DBpedia.
I tried multiple things without success.
This page shows the universities of Paris on the dbo:campus property, so I like to get the list of the universities with this property and after that get the geographics coordinates.
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT ?name, ?univ, ?lat, ?long WHERE {
?p rdf:type dbo:Place.
?p rdfs:label ?name.
?p dbo:campus ?u.
?u geo:lat ?lat.
?u geo:long ?long.
?u rdfs:label ?univ
FILTER(LANG(?name) = "en").
FILTER(?name = "Paris")
}
I check this post DBpedia SPARQL Query US Universities but it doesn't work with another country.

Answer 1

If you read "is SOME_PROPERTY of"on a rendered DBpedia page, this means the inverse direction, i.e., it shows the triple in its inverted form. Thus, you have to invert the triple pattern in the SPARQL query. For your example, it means that universities are the subject and Paris the object:
?u dbo:campus ?p
The labels are language tagged in DBpedia; thus, FILTER(?name = "Paris") is not enough. Adding the English language tag helps:
FILTER(?name = "Paris"#en)
A working query would be
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT ?name, ?univ WHERE {
?p rdf:type dbo:Place.
?p rdfs:label ?name.
?u dbo:campus ?p.
?u geo:lat ?lat.
?u geo:long ?long.
?u rdfs:label ?univ
FILTER(LANG(?name) = "en").
FILTER(?name = "Paris"#en)
}
Some comments:
Using the label to match a resource can lead to unwanted results. Resources are identified by URIs; thus, use the URI if possible. The VALUES clause is a cool feature of SPARQL 1.1 to support inline data.
If you use the URI, you could omit the rdf:type triple pattern since you wouldn't have to filter for resources of a specific type given the label.
The official SPARQL standard doesn't allow commas in between the projection variables; this is Virtuoso-specific syntax.
SPARQL supports the more compact Turtle syntax.
A FILTER doesn't need a . at the end.
Try to use LANGMATCHES for matching languages in literals.
A "better" query could be:
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbr: <http://dbpedia.org/resource/>
SELECT ?name ?univ ?lat ?long
WHERE
{ VALUES ?p { dbo:Paris }
?p rdfs:label ?name .
?u dbo:campus ?p ;
geo:lat ?lat ;
geo:long ?long ;
rdfs:label ?univ
FILTER langMatches(lang(?name), "en")
}