I try to get some data about a city using Sparql query on DBpedia. The problem is I can't get the query to work.
Currently I do something like this:
SELECT ?title,?name,?abs WHERE {
?title skos:subject
<http://dbpedia.org/resource/Category:Cities%2C_towns_and_villages_in_Slovenia>.
?title dbpprop:officialName ?name.
?title dbpprop:abstract ?abs
}
I get all the towns, villages from Slovenia with all the data. The problem is, I would like to get the data (officialName and/or abstract) only for one town, for example Ljubljana. So I tried some things like this:
SELECT ?name WHERE {
?name dbpprop:officialName
<http://dbpedia.org/resource/Ljubljana>.
}
Of course it does not work. I don't exactly know why, though :), but I've been experimenting a bit and noticed some things like if I put
?name skos:subject <http://dbpedia.org/resource/Category:Ljubljana>.
I get some results (which are not relevant to me, but anyway), but if I put
?name skos:subject <http://dbpedia.org/resource/Ljubljana>.
there are no results for anything though element skos:subject exists on the page http://dbpedia.org/resource/Ljubljana.
Could someone please explain why the second example does not work and how to get the result I would like to have?
Thanks,
Ablak
Thanks
You want to query for <http://dbpedia.org/resource/Ljubljana> as a subject, not an object; this would replace your ?title binding in the SPARQL query, for example:
SELECT ?name, ?abs WHERE {
<http://dbpedia.org/resource/Ljubljana>
skos:subject <http://dbpedia.org/resource/Category:Cities%2C_towns_and_villages_in_Slovenia> ;
dbpprop:officialName ?name ;
dbpprop:abstract ?abs .
}
This is why your graph match ?name skos:subject <http://dbpedia.org/resource/Ljubljana> does not return the expected results; the URI for Ljubljana should be the subject of the statement(s) you want to match.
Related
I am using the following query :
select ?value where { <http://dbpedia.org/resource/Paris> dbpedia-owl:wikiPageRedirects* ?value }
in order to retrieve the wikiPageRedirects property of Paris.
Based on dbpedia Paris has more than 20 redirect links. Why am I only retrieving the first one?
Your direction was wrong.
select distinct *
where {
?x dbpedia-owl:wikiPageRedirects <http://dbpedia.org/resource/Paris>
}
Artemis's answer is right; the "direction" in the query is wrong. It's worth explaining that a bit more, though. On the DBpedia "page", you'll see lots of data like:
dbpedia-owl:area 105400000.000000 (xsd:double)
dbpedia-owl:country dbpedia:France
dbpedia-owl:inseeCode 75056 (xsd:integer)
dbpedia-owl:mayor dbpedia:Anne_Hidalgo
These mean that DBpedia contains triples where these are the predicates and objects. That is, DBpedia contains a triple:
dbpedia:Paris dbpedia-owl:country dbpedia:France
On other hand, you'll also see things like "is … of":
is dbpedia-owl:beatifiedPlace of dbpedia:Daniel_Brottier
is dbpedia-owl:billed of dbpedia:René_Duprée
These mean that dbpedia:Paris the object of triples with these subjects and predicates. E.g., DBpedia contains the triple
dbpedia:René_Duprée dbpedia-owl:billed dbpedia:Paris
The redirects properties that you're seeing are like this:
is dbpedia-owl:wikiPageRedirects of dbpedia:City_of_Love_(city)
dbpedia:Département_de_Paris
dbpedia:Departement_de_Paris
dbpedia:FRPAR
That means that there are a bunch of triples of the form:
?something dbpedia-owl:wikiPageRedirects dbpedia:Paris
and that means that your query needs to be
select ?resource where {
?resource dbpedia-owl:wikiPageRedirects dbpedia:Paris
}
SPARQL results
I am using the following query :
select ?value where { <http://dbpedia.org/resource/Paris> dbpedia-owl:wikiPageRedirects* ?value }
in order to retrieve the wikiPageRedirects property of Paris.
Based on dbpedia Paris has more than 20 redirect links. Why am I only retrieving the first one?
Your direction was wrong.
select distinct *
where {
?x dbpedia-owl:wikiPageRedirects <http://dbpedia.org/resource/Paris>
}
Artemis's answer is right; the "direction" in the query is wrong. It's worth explaining that a bit more, though. On the DBpedia "page", you'll see lots of data like:
dbpedia-owl:area 105400000.000000 (xsd:double)
dbpedia-owl:country dbpedia:France
dbpedia-owl:inseeCode 75056 (xsd:integer)
dbpedia-owl:mayor dbpedia:Anne_Hidalgo
These mean that DBpedia contains triples where these are the predicates and objects. That is, DBpedia contains a triple:
dbpedia:Paris dbpedia-owl:country dbpedia:France
On other hand, you'll also see things like "is … of":
is dbpedia-owl:beatifiedPlace of dbpedia:Daniel_Brottier
is dbpedia-owl:billed of dbpedia:René_Duprée
These mean that dbpedia:Paris the object of triples with these subjects and predicates. E.g., DBpedia contains the triple
dbpedia:René_Duprée dbpedia-owl:billed dbpedia:Paris
The redirects properties that you're seeing are like this:
is dbpedia-owl:wikiPageRedirects of dbpedia:City_of_Love_(city)
dbpedia:Département_de_Paris
dbpedia:Departement_de_Paris
dbpedia:FRPAR
That means that there are a bunch of triples of the form:
?something dbpedia-owl:wikiPageRedirects dbpedia:Paris
and that means that your query needs to be
select ?resource where {
?resource dbpedia-owl:wikiPageRedirects dbpedia:Paris
}
SPARQL results
I need to find all DBpedia categories and articles that their abstract include a specific word.
I know how to write a SPARQL query that queries the label like the following:
SELECT ?uri ?txt WHERE {
?uri rdfs:label ?txt .
?txt bif:contains "Machine" .
}
but I have not figured out yet how to search the abstract.
I've tried with the following but it seems not to be correct.
SELECT ?uri ?txt WHERE {
?uri owl:abstract ?txt .
?txt bif:contains "Machine" .
}
How can I retrieve the abstract in order to query its text?
Since you already know how to search a string for text content, this question is really about how to get the abstract. If you retrieve any DBpedia resource in a web browser, e.g., http://dbpedia.org/resource/Mount_Monadnock (which will redirect to http://dbpedia.org/page/Mount_Monadnock), you can see the triples of which it's a subject or predicate. In this case, you'll see that the property is dbpedia-owl:abstract. Thus you can do things like
select * where {
?s dbpedia-owl:abstract ?abstract .
?abstract bif:contains "Monadnock" .
filter langMatches(lang(?abstract),"en")
}
limit 10
SPARQL results
Instead of visiting the page for the resource, which not endpoints will support, you could have simply retrieved all the triples for the subject, and looked at which ones relate it to its abstract. Since you know the abstract is a literal, you could even restrict it to triples where the object is a literal, and perhaps with a language that you want. E.g.,
select ?p ?o where {
dbpedia:Mount_Monadnock ?p ?o .
filter ( isLiteral(?o) && langMatches(lang(?o),'en') )
}
SPARQL results
This also clearly shows that the property you want is http://dbpedia.org/ontology/abstract. When you have a live query interface that you can use to pull down arbitrary data, it's very easy to find out what parts of the data you want. Just pull down more than you want at first, and then refine to get just what you want.
I'm trying to extract alumni lists for universities using SPARQL.
I've identified the ontologies I need:
http://mappings.dbpedia.org/server/ontology/classes/University
http://mappings.dbpedia.org/server/ontology/classes/Person
I tried this query, which you can examine here:
SELECT * WHERE {
?University dbpedia2:alumni ?Person .
}
Which seemed to make sense, except this returns counts instead of people, as the ontology says the property contains.
I found this query somewhere which seemed to do a better job finding universities, but was very slow.
SELECT * WHERE {
{ <http://dbpedia.org/ontology/University> ?property ?hasValue }
UNION
{ ?isValueOf ?property <http://dbpedia.org/ontology/University> }
}
I also tried going the other way, start with all people and look for their almae matres, in this form:
SELECT * WHERE {
?person dbpedia2:almaMater ?University
}
But this is much slower, possibly because searching through the people space is too laborious. This does actually work, but it returns a different set of results in application---namely, all people with a listed alma mater, rather than all people listed by universities as alumni. I'd prefer a syntax that gets me the alumni.
How can I phrase this to return all alumni listed for universities?
The performance of DBpedia's SPARQL endpoint can be a bit unreliable at times. After all, it's apublic service, and isn't intended for huge queries. Nonetheless, I think you can get what you're looking for here without too much trouble. First, you can check how many results there are with a query like this at the public SPARQL endpoint:
select (count(*) as ?nResults) where {
?person dbpedia-owl:almaMater ?almaMater
}
SPARQL results (64928)
Now, if you just want the big list, you'd get it like this. The order by helps organize the results for easy consumption, but isn't technically necessary:
select ?almaMater ?person where {
?person dbpedia-owl:almaMater ?almaMater
}
order by ?almaMater ?person
SPARQL results
If you need to place some additional restrictions on ?almaMater, e.g., to ensure that it's a university, then you can add them to the query. For instance:
select ?almaMater ?person where {
?person dbpedia-owl:almaMater ?almaMater .
?almaMater a dbpedia-owl:University .
}
order by ?almaMater ?person
SPARQL results
In your last query, you are almost there. However, you are currently asking for any resource that can take the place of the ?University variable. As you only want universities to take that place, you can use another triple to further restrict that variable:
SELECT * WHERE {
?University a dbpedia-owl:University.
?person dbpedia2:almaMater ?University.
}
This means that ?University can only be an individual of class dbpedia-owl:University (where dbpedia-owl is mapped to http://dbpedia.org/ontology/).
Your first query:
SELECT * WHERE {
?University dbpedia2:alumni ?Person .
}
isn't just returning counts; it's returning both counts and individual alumni. Apparently dbpedia's data here is poor quality and there are a number of triples misusing the dbpedia2:alumni relation.
You can filter out the counts by adding a second condition requiring that an entity satisfying Person be a member of the appropriate class:
SELECT * WHERE {
?university dbpedia2:alumni ?person .
?person rdf:type <http://dbpedia.org/ontology/Person>
}
What you see running this is that there are very few individuals tagged as alumni; the data is surprisingly scant, unfortunately.
I'm trying to get details about an artist via DBPedia and the SPARQL query language, however, it seems almost impossible (with my understanding) of how to get certain pieces of information.
I'm trying to get an Artist and pull information such as their Hometown. I'm guessing the query should be something similar to that of:
SELECT ?c WHERE {
?b <http://dbpedia.org/property/Artist> <http://dbpedia.org/resource/Arctic_Monkeys>.
?b <http://www.w3.org/2002/07/owl#ObjectProperty> <http://dbpedia.org/ontology/hometown>.
?b rdfs:label ?c.
}
If anyone could enlighten me to how it should be done, that would be amazing.
I've been trying out the queries at:
http://dbpedia.org/sparql
If you want to find the label of their hometown, try this:
SELECT ?hometownLabel WHERE {
<http://dbpedia.org/resource/Arctic_Monkeys> <http://dbpedia.org/ontology/hometown> ?hometown .
?hometown <http://www.w3.org/2000/01/rdf-schema#label> ?hometownLabel .
}
Maybe you don't have a good understanding of SPARQL syntax. Unlike SQL, SPARQL search results by writing some triples with unknow variables in the WHERE clause.
you can try:
prefix dbpedia-owl:<http://dbpedia.org/ontology/>
SELECT ?c
WHERE {
<http://dbpedia.org/resource/Arctic_Monkeys> dbpedia-owl:hometown ?c.
}
With this search, you will get Arctic_Monkeys' hometown.
SELECT ?hometown
WHERE {
dbr:Arctic_Monkeys dbo:hometown ?label.
?label rdfs:label ?hometown.
FILTER(langMatches(lang(?hometown), "en"))
}