this is tutorial that i have follow
我遵循了一些基本的protege教程...但是我从未从sparql中得到结果...
执行时，结果始终为空。即使我完全按照本教程进行操作。
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX ex: <http://www.semanticweb.org/rosel/ontologies/2019/2/nyoba#>
SELECT ?subject ?object
WHERE { ex:tania ex:enroll ?object }