SPARQL query universities
Question
I am trying to fetch the names of universities using SPARQL:
The rdf data is the following (and a whole lot more, but that is irrelevant).
<Organization rdf:about="http://data.semanticweb.org/organization/the-university-of-queensland">
<rdfs:label>The University of Queensland</rdfs:label>
<homepage rdf:resource="http://www.uq.edu.au/"/>
<member rdf:resource="http://data.semanticweb.org/person/jane-hunter"/>
<member rdf:resource="http://data.semanticweb.org/person/kwok-cheung"/>
<member rdf:resource="http://data.semanticweb.org/person/robert-m-colomb"/>
<name>The University of Queensland</name>
</Organization>
I have written a java program which queries the data. My string to query the data is the following:
queryString += "PREFIX swrc: <http://swrc.ontoware.org/ontology#> \n";
queryString += "PREFIX dc: <http://purl.org/dc/elements/1.1/> \n";
queryString += "PREFIX foaf: <http://xmlns.com/foaf/0.1/> \n";
queryString += "PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> \n";
queryString += "PREFIX ical: <http://www.w3.org/2002/12/cal/ical#> \n";
queryString += "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> \n";
queryString += "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> \n";
queryString += "PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#> \n";
queryString += "PREFIX swrc_ext: <http://www.cs.vu.nl/~mcaklein/onto/swrc_ext/2005/05#> \n";
queryString += "SELECT ?name WHERE {\n";
queryString += "?university rdfs:label ?aff . \n ?university foaf:name ?name FILTER(str(?aff)='uni') }";
Unfortunately, this is not correct, as no result is returned:
<?xml version='1.0' encoding='UTF-8'?>
<sparql xmlns='w3.org/2005/sparql-results#'>
<head>
<variable name='name'/>
</head>
<results>
</results>
</sparql>
Can anyone point me in the right direction?
PS If possible I'd like to only fetch 10 university names.
2 answers
solution1
7 ACCPTED 2012-10-28 14:24:40
I understand that you're assuming all universities have the string "uni" in their names.
Notice that you're checking for equality of a value with the string "uni" . There really is no such instance in your data set.
Replacing FILTER(str(?aff)='uni') with FILTER regex(?aff, "uni", "i") will allow you to match the values that contain the string "uni " instead. It's a regular expression filter that takes three arguments.
- a variable
- a regular expression compliant with the syntax described here
- a set of optional flags, in this case, I used one flag,
"i". It means the match must be case-insensitive.
In order to limit the number of results, you can just append the query with the LIMIT keyword.
The resulting query should be:
PREFIX swrc: <http://swrc.ontoware.org/ontology#>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX ical: <http://www.w3.org/2002/12/cal/ical#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>
PREFIX swrc_ext: <http://www.cs.vu.nl/~mcaklein/onto/swrc_ext/2005/05#>
SELECT ?name WHERE {
?university rdfs:label ?aff .
?university foaf:name ?name
FILTER regex(?aff, "uni", "i")
} LIMIT 10;
solution2
-1 2016-10-27 05:56:47
In your RDF snippet does not have the "foaf:" namespace. So, maybe you should put in your RDF. Unless of course it is the default namespace in your RDF document.
solution3
-2 2019-10-15 12:32:02
您编写的代码确实对每个人都有帮助，使每个人都惊讶地理解了惊人的代码。
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