Sparql: getting all politicians who ruled a city - sparql

Question

I'm new to sparql and I'm trying to understand how to get the resources I need for building a query. I started trying to get all the politicians that ruled a city or a country, and at the moment I could do just the following:
I started by following the links in snorql (in the prefixes) and looking for an entity by adding "politician" at the end. I found one :
PREFIX : <http://dbpedia.org/resource/>
So I wrote http://dbpedia.org/resource/Politician and the resource does exist. I tryed to use it in this way:
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbpedia: <http://dbpedia.org/resource/>
SELECT ?thing WHERE {
?thing a :Politician .
?thing dbo:birthPlace dbpedia:Italy.
}
LIMIT 50
Run in virtuoso.
Even if I remove the second line of the SELECT, I have no results. But if I change the first line with: ?thing a dbo:Person. or even if I remove it, I get the people born in Italy. But not just the politicians. A second problem is I don't need the politicians that were born but ruled that place. How or where can I find that kind of "relations/descriptors"? Now I am just googling and copy-pasting some existing examples, but I would like to understand how to look for more specific things.
Thanks in advance

Answer 1

Your first query isn't working because Politician is not part of the default (:) namespace, but instead it is present in DBpedia Ontology namespace (dbo).
So, your query should be:
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbpedia: <http://dbpedia.org/resource/>
SELECT ?thing WHERE {
?thing a dbo:Politician .
?thing dbo:birthPlace dbpedia:Italy.
}
LIMIT 50
To list all politician who ruled Italy you would need to know which is the predicate for "ruled". Once you have it you can construct a query.
To list all predicates present in the database you can write something like this
SELECT DISTINCT(?b) WHERE {
?a ?b ?c.
}
And it will list all predicates.
I would recommend you to browse through one or two politician and see the predicates they have to check if one works for you.