getLiteral在使用jena读取RDF文件时返回null

Question

这些天来我一直在读关于OWL本体和RDF文件的文章。我还是不能理解这一点。

假设我使用Protege创建了一个简单的本体。它有一个称为Review的类，具有两个数据属性，即comment和rating。

<?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>

  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();
        }

后面的行返回NULL。

Literal name = soln.getLiteral("review");

这里面有什么问题？

Answer 1

rdf：id需要解析为绝对IRI，但文件中没有xmlns：base。或者添加一个，或者使用带有绝对虹膜的rdf：about，例如“C：Me”。