On Mon, Apr 20, 2015 at 1:18 PM Markus Krötzsch <markus@semantic-mediawiki.org> wrote:

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


_______________________________________________
Wikidata-l mailing list
Wikidata-l@lists.wikimedia.org
https://lists.wikimedia.org/mailman/listinfo/wikidata-l