Hi all,

For many years, Denny and I have been giving talks about why we need to improve the data management in Wikipedia. To explain and motivate this, we have often asked the simple question: "What are the world's largest cities with a female mayor?" The information to answer this is clearly in Wikipedia, but it would be painfully hard to get the result by reading articles.

I recently had the occasion of actually phrasing this in SPARQL, so that an answer can now, finally, be given. The query to run at

http://milenio.dcc.uchile.cl/sparql

is as follows (with some explaining comments inline):

PREFIX : <http://www.wikidata.org/entity/> SELECT DISTINCT ?city ?citylabel ?mayorlabel WHERE {
 ?city :P31c/:P279c* :Q515 .  # find instances of subclasses of city
 ?city :P6s ?statement .      # with a P6 (head of goverment) statement
 ?statement :P6v ?mayor .     # ... that has the value ?mayor
 ?mayor :P21c :Q6581072 .     # ... where the ?mayor has P21 (sex or gender) female
 FILTER NOT EXISTS { ?statement :P582q ?x }  # ... but the statement has no P582 (end date) qualifier

 # Now select the population value of the ?city
 # (the number is reached through a chain of three properties)
 ?city :P1082s/:P1082v/<http://www.wikidata.org/ontology#numericValue> ?population .

 # Optionally, find English labels for city and mayor:
 OPTIONAL {
   ?city rdfs:label ?citylabel .
   FILTER ( LANG(?citylabel) = "en" )
 }
 OPTIONAL {
   ?mayor rdfs:label ?mayorlabel .
   FILTER ( LANG(?mayorlabel) = "en" )
 }
} ORDER BY DESC(?population) LIMIT 100

To see the results, just paste this into the box at
http://milenio.dcc.uchile.cl/sparql and press "Run query".

The query does not filter the most recent population but relies on Virtuoso to pick the biggest value for DESC sorting, and on the world to have (mostly) cities with increasing population numbers over time. This is also the reason why the population is not printed (it would give you more than one match per city then, even with DISTINCT). Picking the current population will become easier once ranks are used more widely to mark it.

There might also be some inaccuracies in cases where a past mayor does not have an "end date" set in Wikidata (Madrid has a suspiciously large number of current mayors ...), but a query can only ever be as good as its input data.

I hope this is inspiring to some of you. One could also look for the world's youngest or oldest current mayors with similar queries, for example.

Cheers,

Markus


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