Question: Who is the current Chief Justice of the court system that includes William Johnson?
Answer(s):
answer: John Roberts

SPARQL query:
PREFIX ns: <http://rdf.freebase.com/ns/>
SELECT DISTINCT ?x
WHERE {
FILTER (?x != ?c)
FILTER (!isLiteral(?x) OR lang(?x) = '' OR langMatches(lang(?x), 'en'))
?c ns:law.court.judges ?k .
?k ns:law.judicial_tenure.judge ns:m.01hksb . 
?c ns:law.court.judges ?y .
?y ns:law.judicial_tenure.judge ?x .
?y ns:law.judicial_tenure.title ns:m.07szk .
FILTER(NOT EXISTS {?y ns:law.judicial_tenure.from_date ?sk0} || 
EXISTS {?y ns:law.judicial_tenure.from_date ?sk1 . 
FILTER(xsd:datetime(?sk1) <= "2015-08-10"^^xsd:dateTime) })
FILTER(NOT EXISTS {?y ns:law.judicial_tenure.to_date ?sk2} || 
EXISTS {?y ns:law.judicial_tenure.to_date ?sk3 . 
FILTER(xsd:datetime(?sk3) >= "2015-08-10"^^xsd:dateTime) })
}