PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX movie: <http://data.linkedmdb.org/resource/movie/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX yago: <http://yago-knowledge.org/resource/>
PREFIX qb: <http://purl.org/qb4olap/cubes#>
PREFIX schema: <http://qweb.cs.aau.dk/airbase/schema/>
PREFIX property: <http://qweb.cs.aau.dk/airbase/property/>
PREFIX country: <http://qweb.cs.aau.dk/airbase/data/country/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT sum(?ratio) WHERE {
SELECT DISTINCT (xsd:float(?p)/xsd:float(?gp) AS ?ratio) ?avgo3 WHERE {
{  
           SELECT ?city ?p ?gp WHERE {
             ?c schema:locatedIn <http://qweb.cs.aau.dk/airbase/data/country/Greece/> .
             ?c owl:sameAs ?city .
             SERVICE <https://linkeddata1.calcul.u-psud.fr/sparql> {     
               ?city yago:hasNumberOfPeople ?p . FILTER (?p > 0)
                yago:Greece yago:hasNumberOfPeople ?gp .
             }
          } 
}
{
   SELECT ?city (max(?o3) as ?avgo3) WHERE {   
      ?obs schema:O3 ?o3 .
      ?obs schema:station ?st .
      ?obs schema:sensor ?sn .
      ?sn property:statisticShortName "Max"^^xsd:string .
      ?st schema:inCity ?c .
      ?obs schema:year ?year .
      ?year property:yearNum "2011"^^xsd:decimal .
      ?c schema:locatedIn <http://qweb.cs.aau.dk/airbase/data/country/Greece/> .
      ?c owl:sameAs ?city .        
    } GROUP BY ?city HAVING (max(?o3) > 18)
}
}}