Question: What is the highest volcano in Africa?
SPARQL query:
PREFIX onto: <http://dbpedia.org/ontology/>
PREFIX res: <http://dbpedia.org/resource/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX yago: <http://dbpedia.org/class/yago/> 
SELECT DISTINCT ?uri 
WHERE {
        ?uri rdf:type onto:Volcano .
        ?uri onto:locatedInArea ?area .        
        ?area rdf:type yago:AfricanCountries . 
        ?uri onto:elevation ?elevation .
}
ORDER BY DESC(?elevation) 
OFFSET 0 LIMIT 1