How many {has quality} are to/by {stiffness} ?
What is the number who have quality stiffness?
How many have quality stiffness?
SELECT ( COUNT ( ?f ) AS ?h ) { ?f property:has_quality resource:stiffness }
SELECT (COUNT(?sub) AS ?subs ) {
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> ?sub .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <http://www.wikidata.org/entity/P1552> .
?statement <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> http://wikidata.dbpedia.org/resource/Q569057 .
} 

SELECT (COUNT(?sub) AS ?value ) { ?sub wdt:P1552 wd:Q569057 }
7