Question: Which position has the highest average salary in Washington DC?
SPARQL:
 select ?result from <http://linkedspending.aksw.org/dc-city-salaries> { ?obs qb:dataSet ls:dc-city-salaries. ?obs lso:dc-city-salaries-amount ?amount. ?obs lso:dc-city-salaries-position ?result. } order by desc(avg(xsd:decimal(?amount))) limit 1