Question: Count the number of books whose author's were born in Alcal de Henares ?
SPARQL:
SELECT DISTINCT COUNT(?uri) WHERE { ?x <http://dbpedia.org/ontology/birthPlace> <http://dbpedia.org/resource/Alcalá_de_Henares> . ?uri <http://dbpedia.org/ontology/author> ?x  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Book>}