I have been reading about OWL ontology and RDF files all these days. I still can't understand this.
Let's say I created a simple ontology using Protege. It has single class called Review with two data properties which are comment and rating.
Now I want to create a separate RDF file written in xml which has some comments. The file I created look like
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:c="http://review-analyzer.local/ontologies/reviews_2.owl#">
<rdf:Description rdf:ID="me">
<c:review>Display looks amazing!</c:review>
<c:raitng>5</c:raitng>
</rdf:Description>
<rdf:Description rdf:ID="me2">
<c:review>Display is great!</c:review>
<c:raitng>5</c:raitng>
</rdf:Description>
</rdf:RDF>
Now I want to read this file into jena model, read this reviews and create individuals in my ontology. Creating individual part I already have figured out. But I can't get rating and comment values from these reviews.
The code I have tried is
Model model = ModelFactory.createOntologyModel();
model.read("./rdf/119.rdf", "RDF/XML");
String queryString =
"PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>\r\n" +
"PREFIX ns: <http://review-analyzer.local/ontologies/reviews_2.owl#>"+
"select *\r\n" +
"where {\r\n" +
" ?Comment ns:review ?review .\r\n" +
" ?Comment ns:raitng ?raitng .\r\n" +
"}";
Query query = QueryFactory.create(queryString);
QueryExecution qexec = QueryExecutionFactory.create(query, model);
try {
ResultSet results = qexec.execSelect();
List<String> varNames = results.getResultVars();
while (results.hasNext()) {
QuerySolution soln = results.nextSolution();
Literal name = soln.getLiteral("review");
System.out.println(soln);
}
} finally {
qexec.close();
}
Following line returns null.
Literal name = soln.getLiteral("review");
What's the problem in this?