SPARQL in DBpedia return no results

I try to write a query in SPARQL in DBpedia to return all the info for high schools in a certain country. I run the query on snorql here link, but it returns "no results". I cannot find any error on my query. Can anyone help?

SELECT ?school
WHERE { 
?school a owl:school. 
?school owl:location ?city. 
?city owl:isPartOf ?state. 
?state owl:country <http://dbpedia.org/resource/United_States>.
}

Edit:

Solution

You seem to be mistaken about the ontologies you should be using. You are using various identifiers from the namespace mapped to the prefix owl, namely:

owl:school
owl:location
owl:isPartOf
owl:country

However, as you do not specify a custom prefix mapping, the default mapping is used, according to which owl is mapped to http://www.w3.org/2002/07/owl#, which is OWL 2. OWL 2 does not contain any definitions for the listed identifiers, and DBpedia accordingly does not use these identifiers.

DBpedia does use the identifiers School, location, isPartOf and country from the namespace http://dbpedia.org/ontology/, which is mapped to the prefix dbpedia-owl. Therefore, in your query, just use the prefix for the ontology you actually want to use. Furthermore, note that the class dbpedia-owl:School is capitalized, dbpedia-owl:school with a small s is a property.

SELECT ?school
WHERE { 
    ?school a dbpedia-owl:School. 
    ?school dbpedia-owl:location ?city. 
    ?city dbpedia-owl:isPartOf ?state. 
    ?state dbpedia-owl:country <http://dbpedia.org/resource/United_States>.
}