SPARQL query for dbpedia to find ski lifts - sparql

Question

I'm currently trying to teach myself how to formulate SPARQL queries to extract tourism-related information from DBpedia (via http://dbpedia.org/sparql/).
So far, I've managed to get all museums for a country.
select ?thing ?type ?category ?long ?lat ?country
where
{
VALUES ?country { <http://dbpedia.org/resource/Canada> }
optional
{
?city dbo:country ?country
}
?thing dbo:location ?city.
optional
{
?thing a ?type .
VALUES ?type { dbo:Museum }
BIND( 'Museum' as ?category )
}
optional
{
?thing a ?type.
VALUES ?type { dbo:skiLift }
BIND( 'Skilift' as ?category )
}
optional
{
?thing geo:long ?long.
?thing geo:lat ?lat
}
{
?thing a dbo:Place
}
filter (BOUND (?type))
}
However, I don't understand what I need to do to also get the same information for things like dbo:skiLift, dbo:touristicSite and the like (found here: http://dbpedia.org/ontology/Place).
What am I doing wrong?

Answer 1

This is because both dbo:skiLift and dbo:touristicSite are properties. These resources show up in the page for Place not as subclasses of Place, but as properties which have the class Place as their domain or range. If you want to find subclasses of Place you can perform the exploratory query (which also uses property path to retrieve the transitive closure of the subClassOf property):
select ?thing
where
{
?thing rdfs:subClassOf+ <http://dbpedia.org/ontology/Place> .
}
Apart from that, I cannot understand why you use two optional clauses for different types in the same query. For example, the following query retrieves museums located at cities of Canada, possibly with their lat and lon, without the use of other optional clauses:
select ?thing ?city ?long ?lat
where
{
?city dbo:country <http://dbpedia.org/resource/Canada> .
?thing dbo:location ?city .
?thing a dbo:Museum .
optional
{
?thing geo:long ?long .
?thing geo:lat ?lat
}
}