SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/source> <http://dbpedia.org/resource/Lake_Ontario> . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}
What is the river whose source is Lake Ontario?
SELECT DISTINCT ?p WHERE { ?p rdf:type ontology:River . ?p property:source resource:Lake_Ontario }
Saint Lawrence River
The river whose origin is Lake Ontario is [Saint Lawrence River].
The river originates in Lake Ontario [the St. Lawrence River].
The river whose source is Lake Ontario is  [St. Lawrence River].
The river, which originates in Lake Ontario, is [St. Lawrence River].