What is the {operating system} for {developer} of {Dennis M. Ritchie}
What did Dennis M. Ritchie develop?
What operating system did Dennis M. Ritchie develop?
SELECT DISTINCT ?z WHERE { ?z property:developer resource:Dennis_M._Ritchie . ?z rdf:type ontology:operating_system }
select distinct ?subj where { ?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?subj . ?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P178> . ?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <http://wikidata.dbpedia.org/resource/Q45575> . ?subj <http://www.wikidata.org/entity/P31> <http://wikidata.dbpedia.org/resource/Q9135> } 
 select distinct ?sbj where { ?sbj wdt:P178 wd:Q45575 . ?sbj wdt:P31 wd:Q9135 } 