(This page is still under construction.)


Some help (such as sample SPARQL queries) can be found on answers.semanticweb.com and/or Stack Overflow. The most recent 10 posts for each site should be seen in the Feeds section, lower down on this page. Full searches are linked here --


If the information you need cannot be found there, you can:

  1. create a new post on one of the Overflow sites and use the tag “dbpedia”
  2. check the DBpedia support page .

Feeds

(Still not displayed correctly, we are working on aggregating the feed)

answers.semanticweb.com

DBpedia entities, classes and ontology

Hi,

I'm trying to figure out how DBpedia entities are classified considering only the its ontology. Typically, an entity E is classified with N classes that belong to the same branch in the ontology hierarchy. For instance the entity http://dbpedia.org/resource/Galileo_Galilei is classified using owl:Thing, Person, Scientist that are connected by rdfs:subClassOf in the same branch. owl:Thing <- Person <- Scientist. What if Galileo has also the class Painter? It is possible to have this kind of situation? How can i check it?

This answer was similar but takes into consideration also other ontologies such as YAGO, schema.org, etc... while here I'm considering only the DBpedia Ontology.

Thank you

Entity linking database relation model (Based on dbpedia)

I am trying to come up with a model for a knowledge database to solve the problem of entity linking. The knowledge database is composed of the following tables. What do you think of this design? Is there something missing or any suggestion? Do you agree with the terminologies


  • Entity: Uniquely identifiable thing or object. It has the following attributes: ID, Name, Type {Person, Organization, Place}, Title, Document {wiki page associated with the entity}

  • Variations: Name variations of the entity {different languages} that refer to the same entity. An entity can have 1 to many variations. A Variation can refer to 1 or many entities.Vladimir putin #SameAs enter image description here

  • Co-reference: Different names that refer to the same entity Michael Jordan #wikiPageRedirects

enter image description here

  • Relations: Relations between entities in the knowledge database. An entity can have 1 to many relations. A relation can refer to 1 or many entities. enter image description here

enter image description here

How the pass the output of one sparql query as a input to another sparql query.

Query1:

 prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>
    prefix dbpedia-owl: <http://dbpedia.org/ontology/>
     SELECT  *WHERE
        {   
        { 
      select distinct ?film where  {
      ?film a dbpedia-owl:Film .
      ?film rdfs:label ?label .
      filter regex( str(?label), "Lagaan", "i")
      }
      limit 10
   }

Query2:

PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>
        select ?similar (count(?p) as ?similarity) where { 
          values ?movie { <http://dbpedia.org/resource/Lagaan> }
          ?similar ?p ?o ; a dbpedia-owl:Film .
          ?movie   ?p ?o .
        }
        group by ?similar ?movie
        having count(?p) > 35
        order by desc(?similarity)

So what i am trying to do is get the dbpedia movie link using the movie name in the first query and pass that link in the second query to get the movies similar to this movie.For e.g Lagaan.Now instead of passing the link manually in the second query is there a way to combine the two queries and ouput of first query is passed as input to the second query.i.e:the link of the movie lagaan.

Getting an exception while executing the SPARQL Query

Hi All,

I am very new to this language. I am trying to executing a SPARQL query and I observed a weird behavior. Here is the example:

SELECT (Count (DISTINCT ?Name) AS ?result) WHERE 
{ 
  ?x foaf:givenName ?FirstName;
  foaf:surname ?LastName;
  rdfs:label ?Name;
  dbpedia-owl:birthDate ?dob;
  dbpedia-owl:abstract ?abstract;
  dbpprop:shortDescription ?sh.
  FILTER(LANGMATCHES(LANG(?Name), "en"))
}

Here are the problems:

  1. I executed this query multiple times and each time I got different results (the count). I don't know why I am getting this kind of weird behavior...???
  2. I added another FILTER to the aforementioned query and I am getting the below exception.

Exception: Virtuoso 42000 Error The estimated execution time 120 (sec) exceeds the limit of 120 (sec).

I don't know how to overcome these issues. Can some one spread the light on these issues...???

Thanks & Regards, Amar

DBPedia resource - timestamp

Hi,

Is there currently any way to get a timestamp about a DBPedia resource as http://dbpedia.org/resource/Europe

The goal would be, in a scenario where a local copy of a resource is needed, to detect that a newer version has been published and then update the local copy.

It seems that the http-header "last-modified" is empty.

Or could we use the http-header "expires" data, but this doesn't seem to really reflect that the RDF data has been updated, does it ?

I guess there isn't a VoID description available for those linked data accessed from their URL ?

Thank you for any pointer
Fabian

Sparql query on Dbpedia with different languages

I have a wiki page and from the infobox I want to retrieve some specific informations from dbpedia. With respect to dbpedia infobox_properties_definitions available online I'm able to achieve my goal but only under "en" language. An example: the following query works fine ("images shield" comes directly from the infobox page of Pergine_Valsugana ):

select ?value where {
?propName rdfs:label "image shield"@en .
dbpedia:Pergine_Valsugana ?propName ?value
}

but if I try the same for "it" wikipedia page in which "image_shield" is replaced with "Stemma" I dont get any result (I should have one because downloading the infobox_properties_en_uris_it.nt from dbpedia the triple I'm looking for is present and "Stemma" definition as well in infobox_property_definitions_en_uris_it.nt) Here is the query with no result:

select ?value where { 
?propName rdfs:label "Stemma"@it .
dbpedia:Pergine_Valsugana ?propName ?value
}

Thanks

DBpedia Statistics without SPARQL

Hi everyone, I'm trying to make some statistics on the DBpedia Dataset. The first approach I used was making SPARQL queries. It turns out as explained in this previous discussion that Virtuoso is bugged and it is not possible to retrieve the desired numbers. So, in order to overcome the problem I dowloaded DBpedia as Tables for querying the data in a way different from SPARQL.

I want to retrieve which are the numbers of triples that connnect each pair of classes in the Dbpedia ontology. Since the SPARQL approach failed which tools can I use? What do you suggest? MongoDB is a good choice for dealing with this kind of data? What about Neo4j? Is there other solutions? is this the wrong approach?

dbpedia query

Hello all! I want to query dbpedia link text so that it shows the external links of every object separated by "," and i am writing:

SELECT ?x ?title (group_concat(distinct ?ext;separator="; ") as ?exts)
      WHERE 
      {   ?x rdfs:label ?title .
          ?x dbpedia-owl:wikiPageExternalLink ?ext .
      } GROUP BY ?x ?title ?exts
LIMIT 10

But I am getting an error "Virtuoso 37000 Error SP031: SPARQL compiler: Variable 'exts' is used in the query result set but not assigned"

What am i doing wrong?

Update So I've put an "s"

SELECT ?x ?title (group_concat(distinct ?ext;separator="; ") as ?exts)
          WHERE 
          {   ?x rdfs:label ?title .
              **?x dbpedia-owl:wikiPageExternalLink ?exts .**
          } GROUP BY ?x ?title ?exts
    LIMIT 10

but know i am getting the error "Virtuoso 37000 Error SP031: SPARQL compiler: Variable 'ext' is used in the query result set but not assigned"

Thanks again and sorry for my mistake above. I am searching for many external links, not many titles. So the code above is updated.

But it is weird because in this sparql endpoint link text the code words:

PREFIX dct: <http://purl.org/dc/terms/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
select ?c ?s (group_concat(distinct ?y;separator="; ") as ?ys)
FROM <http://data.open.ac.uk/context/oro>
where {?c dct:title ?s .
 ?c dct:creator ?k .
 ?k foaf:name ?y .
}group by ?c ?s ?ys

How to traverse skos:broader property

Any help in my learning will be highly appreciated.

Problem statement:

Need to print list of tourist places in various cities

I have http://dbpedia.org/page/Category:Tourism_by_city category which i have to explore. The problem is this category is a skos:broader of various other categories like http://dbpedia.org/page/Category:Tourism_in_Bratislava which in itself is a skos:broader of http://dbpedia.org/page/Category:Visitor_attractions_in_Bratislava which contains dcterms:subject property and which is the list of tourist places. I have to explore all cities starting from Tourism_by_city category.

Please do let me know if question is unclear. Thanks

bulk loading DBpedia in Virtuoso

I am trying to load dbpedia datasets onto Virtuoso on windows 7.

I use the command ld_dir and I follow it with SELECT * FROM DB.DBA.LOAD_LIST; and it seems to be fine. But once I run the rdf_load_run the laptop keeps beeping and command line freezes, until I close it.

I tried modifying the NumberOfBuffers and the MaxDirtyBuffers in virtuoso.ini but that did not have any effect. I also tried with the quand store upload, but that didnt work either.

Does that mean that the 4 GB RAM I have is not enough to upload it?



 
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Last Modification: 2011-07-24 20:04:59 by Sebastian Hellmann