Re: [Wikidata-l] World's largest cities with a female mayor :-)

On 21.04.2015 02:05, James Douglas wrote:

This is super cool, thanks for sharing! Would you mind if I write it up for the Wikidata Query Service docs?

No, of course not. We could certainly use some more documentation. Be aware, however, that the RDF export format is still subject to change, so the query will have to change accordingly in the future.

Markus

On Mon, Apr 20, 2015 at 3:50 PM, Markus Krötzsch <markus@semantic-mediawiki.org mailto:markus@semantic-mediawiki.org> wrote:

On 20.04.2015 23:47, Daniel Kinzler wrote:

    Something seems to be wrong with the order, though. Munich (pop
     > 1m in all
    statements) is listed way after Chemnitz (pop < 300k in all
    statements). Any
    idea why?


Good catch. My query was too simple (using one "random" population
instead of the biggest one). Here is a better query, this time even
with populations given:

PREFIX : <http://www.wikidata.org/entity/>
SELECT ?city (MAX(?population) AS ?max_population)  ?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" )
  }
} GROUP BY ?city ?citylabel ?mayorlabel
ORDER BY DESC(?max_population) LIMIT 100


    Oh... maybe quantity values are sorted in alphanumeric order,
    because they are
    decimal strings? They should be xsd:decimal...


They are.

Markus



    Am 20.04.2015 um 22:18 schrieb Markus Krötzsch:

        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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