I'm working with an ontology OWL and making a query about it.
My query is:
"PREFIX a: http://www.owl-ontologies.com/Indoor.owl# "
+ "SELECT ?X "
+ "WHERE { ?X a:hasDay a:" + day + " . "
+ " ?X a:hasRoom a:" + room + " . "
+ " ?X a:hasStartTime a:" + startTime +" }";
At the moment to make the query, the console of NetBeans throw me:
Undefined object property used in query: http://www.owl-ontologies.com/Indoor.owl#hasStartTime
But hasStartTime in the ontology isn't an object property, it is a data type (int).
Assuming that the value of the Java variable startTime is e.g. 420 (7am), if you look at your SPARQL query, the last triple pattern is made by
?X a:hasStartTime a: plus value of ``startTime,
i.e. it results in
?X a:hasStartTime a:420
RDF literals have to be put in quotes without a prefix - it's a literal and not a prefixed URI, e.g.
?X a:hasStartTime 420
or to make the datatype more explicit (for integer values the above is just a shortcut)
?X a:hasStartTime "420"^^<http://www.w3.org/2001/XMLSchema#integer>
Related
I wrote SPARQL in String queryString
"SELECT DISTINCT ?dog ?p ?o " +
"WHERE {" +
"?dog <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://test#dog>. " +
"?dog ?p ?o. " +
"}";
...
while (rs_s.hasNext()) {
QuerySolution qs = rs_s.next();
String s1 = qs.get("dog").toString();
String s2 = qs.get("p").toString();
String s3 = qs.get("o").toString();
As a result, I got a triple format.
How do I get it with RDF XML?
I'm tring to find informations about a place (ex : New York http://dbpedia.org/page/New_York). I' try to get informations suchs as nearestCity , museum)...
My request returns nothing...
String name = "New_York";
String s4 = "PREFIX g: <http://www.w3.org/2003/01/geo/wgs84_pos#>\n" +
"PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n" +
"PREFIX onto: <http://dbpedia.org/ontology/>\n" +
"PREFIX dbpedia: <http://dbpedia.org/resource/>PREFIX dcterms: <http://purl.org/dc/terms/>\n"+
"PREFIX dp: <http://dbpedia.org/resource/>\n"+
"PREFIX dbprop: <http://dbpedia.org/property/>\n" +
"PREFIX grs: <http://www.georss.org/georss/>\n"+
"PREFIX dbpedia-oll: <http://dbpedia.org/ontology/> \n"+
"PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>PREFIX category: <http://dbpedia.org/resource/Category:>\n"+
"\n" +
"SELECT ?nearestCity \n" +
"WHERE\n" +
"{ OPTIONAL{onto:"+name+" grs:nearestCity ?nearestCity .}\n"+
" }\n" +
"LIMIT 300\n" +
"";
There are a couple problems with the query you are doing:
1) Some namespaces are wrong: the resource New_York has the URI: http://dbpedia.org/resource/New_York. In your query that would translate to "dbpedia:"+name instead of "onto:"+name.
2) The properties that you are looking for point to the resource New_York, not the other way around. For example, for the nearest city one, this is the query that works (note the namespaces again for the property):
SELECT ?nearestCity where {
?nearestCity <http://dbpedia.org/property/nearestCity> <http://dbpedia.org/resource/New_York>.
}LIMIT 300
(See results)
And for museum:
SELECT ?m where {
?m <http://dbpedia.org/ontology/museum> <http://dbpedia.org/resource/New_York>.
}LIMIT 300
(See results)
I am using the Jena Java framework for querying DBpedia end point using SPARQL, to get the type for all points of interest in German cities. I am facing no issue for places that have English DBpedia entries. But, when it comes to place names to be queried from the German DBpedia endpoint (http://de.dbpedia.org/resource/Schloß_Nymphenburg), this query returns no result. This problem is also mentioned over here (http://mail-archives.apache.org/mod_mbox/jena-users/201110.mbox/%3C4E877C8A.4050705#apache.org%3E). Even after referring to this, I am unable to solve the problem. I don't know how to work with QueryEngineHTTP. I am adding two code snippets - one that works (first one - query for Allianz Arena : which has an English entry in DBpedia) and one that doesn't work (second one - for Schloß Nymphenburg, that has a German entry).
This might be a very trivial issue, but I am unable to solve it. Any pointers to a solution would be very very helpful.
Thanks a lot!
Code 1 - working :
String service = "http://dbpedia.org/sparql";
final ParameterizedSparqlString query = new ParameterizedSparqlString(
"PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>" +
"PREFIX dbo: <http://dbpedia.org/ontology/>" +
"PREFIX dcterms: <http://purl.org/dc/terms/>" +
"SELECT * WHERE {" +
"?s geo:lat ?lat ." +
"?s geo:long ?long ." +
"?s dcterms:subject ?sub}");
query.setIri("?s", "http://dbpedia.org/resource/Allianz_Arena");
QueryExecution qe = QueryExecutionFactory.sparqlService(service, query.toString());
ResultSet results = qe.execSelect();
ResultSetFormatter.out(System.out, results);
Code 2 - not working :
String service = "http://dbpedia.org/sparql";
final ParameterizedSparqlString query = new ParameterizedSparqlString(
"PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>" +
"PREFIX dbo: <http://dbpedia.org/ontology/>" +
"PREFIX dcterms: <http://purl.org/dc/terms/>" +
"SELECT * WHERE {" +
"?s geo:lat ?lat ." +
"?s geo:long ?long ." +
"?s dcterms:subject ?sub}");
query.setIri("?s", "http://de.dbpedia.org/resource/Schloß_Nymphenburg");
QueryExecution qe = QueryExecutionFactory.sparqlService(service, query.toString());
ResultSet results = qe.execSelect();
ResultSetFormatter.out(System.out, results);
I don't think this is an issue with jena at all. Trying:
SELECT * WHERE {
<http://de.dbpedia.org/resource/Schloß_Nymphenburg> ?p ?o }
at http://dbpedia.org/sparql I get no results: try it yourself.
SELECT * WHERE {
<http://de.dbpedia.org/resource/Schloss_Nymphenburg> ?p ?o }
by contrast returns something, even if it's just a bunch of cross links.
I'm using Jena to make a SPARQL query to search for all a document's properties by its subject. But the documents can have more than one subject, and when I do the search, it doesn't return me all the documents' properties, including all the documents' subjects, but even if it has 3 subjects (for example) it returns me all the documents properties + only the subject I set at FILTER.
I'd like to have as a return all the properties from the found document + all the subjects (that belong to the found document) and not only the one at FILTER.
Query (this.subject is a variable that has its value set in a JSF page):
String queryString = "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> " +
"PREFIX dc: <http://purl.org/dc/elements/1.1/> " +
"PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?document ?subject" +
" ?title ?description ?language WHERE { " +
"?document dc:title ?title." +
"?document dc:subject ?subject." +
"?document dc:description ?description." +
"?document dc:language ?language." +
"FILTER ( regex(?subject, replace( \"" + this.subject + "\", ' ', '|' ), 'i' )). }";
Thank you!
You likely want to use a sub-query to restrict to the documents matching the FILTER and then select the rest of the stuff you are actually interesting in e.g.
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dc : <http://purl.org/dc/elements/1.1/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?document ?subject ?title ?description ?language
WHERE
{
{
SELECT ?document
WHERE
{
?document dc:subject ?subject .
FILTER(REGEX(?subject, REPLACE("search term", " ", "|"), "i"))
}
}
?document dc:title ?title ;
dc:description ?description ;
dc:subject ?subject ;
dc:language ?language .
}
Note that this is still going to give you a row for each document-subject combination so if you have a document with 3 subjects you'll get three rows for that document. If you want to combine documents into a single row then you can use GROUP BY and then a GROUP_CONCAT aggregate, there are other questions already on Stack Overflow that detail how to do that.
Notes
Also note that using simple string concatenation to inject constants into your query is ill advised, take a look at Jena's ParameterizedSparqlString for a more user friendly and SPARQL injection proof API for building queries.
I want to get the latitude and longitude of a place whose name I already know by
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT * WHERE {
?s a dbo:Place .
?s geo:lat ?lat .
?s geo:long ?long .
}
where the name of the place (?s) is something like Graves Park.
How would one go about implementing the same in Jena where the name of the place might vary?
You can use Jena's ARQ to execute queries against remote SPARQL endpoints. The process is described in ARQ — Querying Remote SPARQL Services.
Using ParameterizedSparqlStrings in SELECT queries
To do this for different places that you might not know until it is time to execute the query, you can use a ParameterizedSparqlString to hold the query and then inject the value(s) once you have them. Here's an example. The query is the one you provided. I put it into a ParameterizedSparqlString, and then used setIri to set ?s to http://dbpedia.org/resource/Mount_Monadnock.
import com.hp.hpl.jena.query.ParameterizedSparqlString;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.ResultSet;
import com.hp.hpl.jena.query.ResultSetFormatter;
public class DBPediaQuery {
public static void main( String[] args ) {
final String dbpedia = "http://dbpedia.org/sparql";
final ParameterizedSparqlString queryString
= new ParameterizedSparqlString(
"PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>"+
"PREFIX dbo: <http://dbpedia.org/ontology/>" +
"SELECT * WHERE {" +
" ?s a dbo:Place ." +
" ?s geo:lat ?lat ." +
" ?s geo:long ?long ." +
"}" );
queryString.setIri( "?s", "http://dbpedia.org/resource/Mount_Monadnock");
QueryExecution exec = QueryExecutionFactory.sparqlService( dbpedia, queryString.toString() );
ResultSet results = exec.execSelect();
ResultSetFormatter.out( System.out, results );
}
}
The results printed by this are:
--------------------------------------------------------------------------------------------------------------
| lat | long |
==============================================================================================================
| "42.8608"^^<http://www.w3.org/2001/XMLSchema#float> | "-72.1081"^^<http://www.w3.org/2001/XMLSchema#float> |
--------------------------------------------------------------------------------------------------------------
Once you have the ResultSet, you can iterate through the rows of the solution and extract the values. The values here are Literals, and from a Literal you can extract the lexical form (the string value), or the value as the corresponding Java type (in the case of numbers, strings, booleans, &c.). You could do the the following to print the latitude and longitude instead of using the ResultSetFormatter:
while ( results.hasNext() ) {
QuerySolution solution = results.next();
Literal latitude = solution.getLiteral( "?lat" );
Literal longitude = solution.getLiteral( "?long" );
String sLat = latitude.getLexicalForm();
String sLon = longitude.getLexicalForm();
float fLat = latitude.getFloat();
float fLon = longitude.getFloat();
System.out.println( "Strings: " + sLat + "," + sLon );
System.out.println( "Floats: " + fLat + "," + fLon );
}
The output after this change is:
Strings: 42.8608,-72.1081
Floats: 42.8608,-72.1081
Using ParameterizedSparqlStrings in CONSTRUCT queries
Based some of the comments, it may also be useful to use CONSTRUCT queries to save the results from each query, and to aggregate them into a larger model. Here's code that uses a construct query to retrieve the latitude and longitude of Mount Monadnock and Mount Lafayette, and stores them in a single model. (Here we're just using CONSTRUCT WHERE {…}, so the model that is returned is exactly the same as the part of the graph that matched. You can get different results by using CONSTRUCT {…} WHERE {…}.)
import com.hp.hpl.jena.query.ParameterizedSparqlString;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
public class DBPediaQuery {
public static void main( String[] args ) {
final String dbpedia = "http://dbpedia.org/sparql";
final ParameterizedSparqlString queryString
= new ParameterizedSparqlString(
"PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>"+
"PREFIX dbo: <http://dbpedia.org/ontology/>" +
"CONSTRUCT WHERE {" +
" ?s a dbo:Place ." +
" ?s geo:lat ?lat ." +
" ?s geo:long ?long ." +
"}" );
Model allResults = ModelFactory.createDefaultModel();
for ( String mountain : new String[] { "Mount_Monadnock", "Mount_Lafayette" } ) {
queryString.setIri( "?s", "http://dbpedia.org/resource/" + mountain );
QueryExecution exec = QueryExecutionFactory.sparqlService( dbpedia, queryString.toString() );
Model results = exec.execConstruct();
allResults.add( results );
}
allResults.setNsPrefix( "geo", "http://www.w3.org/2003/01/geo/wgs84_pos#" );
allResults.setNsPrefix( "dbo", "http://dbpedia.org/ontology/" );
allResults.setNsPrefix( "dbr", "http://dbpedia.org/resource/" );
allResults.write( System.out, "N3" );
}
}
The output shows triples from both queries:
#prefix dbr: <http://dbpedia.org/resource/> .
#prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> .
#prefix dbo: <http://dbpedia.org/ontology/> .
dbr:Mount_Lafayette
a dbo:Place ;
geo:lat "44.1607"^^<http://www.w3.org/2001/XMLSchema#float> ;
geo:long "-71.6444"^^<http://www.w3.org/2001/XMLSchema#float> .
dbr:Mount_Monadnock
a dbo:Place ;
geo:lat "42.8608"^^<http://www.w3.org/2001/XMLSchema#float> ;
geo:long "-72.1081"^^<http://www.w3.org/2001/XMLSchema#float> .