Unable to retrieve results from owl using Jena

Question

First of all, I created my own, sample ontology using Protege 4. My actual goal is developing a semantic web application that benefits from object properties to offer something to users. After I created my ontology, I'll add dynamic data, so I need to use *Jena API *. For the sake of demonstration I created sample instances. But when I try to retrieve results, I got nothing.

Maybe I'm missing something in my SPARQL query.

private static final String baseUri = "http://www.semanticweb.org/ontologies/alisveris.owl#";

private static void modelReadFile(String filename, Model model) {
    try {
        File f = new File(filename);
        FileReader fr = new FileReader(f);
        model.read(fr, baseUri);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
}


private static void printModel(Model model) {
    String queryString =
        "PREFIX lib: " +
        "SELECT ?name ?surname " +
        "FROM " +
        "WHERE {" +
        "?name lib:take \"JavaProgramming\" " +
        "}";
    System.out.println(queryString);
    Query query = QueryFactory.create(queryString);
    QueryExecution qe = QueryExecutionFactory.create(query, model);
    ResultSet results = qe.execSelect();
    ResultSetFormatter.out(System.out, results, query);
    qe.close();
}


public static void main(String[] args) {
    Model model = ModelFactory.createDefaultModel();
    modelReadFile("/home/talha/ontologies/alisveris.owl", model);

    // Create properties for the different types of relationship to represent
    Property take = model.createProperty(baseUri, "take");
    Property isTakenBy = model.createProperty(baseUri, "isTakenBy");
    Property published = model.createProperty(baseUri, "published");
    Property publishedBy = model.createProperty(baseUri, "publishedBy");

    // User data properties
    Property userId = model.createProperty(baseUri, "userId");
    Property name = model.createProperty(baseUri, "name");
    Property surname = model.createProperty(baseUri, "surname");
    Property username = model.createProperty(baseUri, "username");
    Property password = model.createProperty(baseUri, "password");
    Property gender = model.createProperty(baseUri, "gender");
    Property age = model.createProperty(baseUri, "age");
    // Publisher data properties
    Property publisherId = model.createProperty(baseUri, "publisherId");
    Property publisherName = model.createProperty(baseUri, "publisherName");
    // Book data properties
    Property bookId = model.createProperty(baseUri, "bookId");
    Property bookName = model.createProperty(baseUri, "bookName");
    Property bookGenre = model.createProperty(baseUri, "bookGenre");
    Property pageCount = model.createProperty(baseUri, "pageCount");
    Property isbn = model.createProperty(baseUri, "isbn");
    Property bookRating = model.createProperty(baseUri, "bookRating");


    Resource talha = model.createResource(baseUri + "Talha");
    Resource javaProgramming = model.createResource(baseUri + "JavaProgramming");
    // and so on for other family members

    talha.addProperty(userId, "1");
    talha.addProperty(name, "Talha");
    talha.addProperty(surname, "Kabakuş");
    talha.addProperty(username, "talhak");
    talha.addProperty(password, "00");
    talha.addProperty(gender, "1");
    talha.addProperty(age, "23");


    javaProgramming.addProperty(bookId, "1");
    javaProgramming.addProperty(publisherId, "1");
    javaProgramming.addProperty(bookName, "Java Programming");
    javaProgramming.addProperty(bookGenre, "1");
    javaProgramming.addProperty(pageCount, "200");
    javaProgramming.addProperty(isbn, "121321312");
    javaProgramming.addProperty(bookRating, "3");

    // Add properties to adam describing relationships to other family members
    talha.addProperty(take, javaProgramming);

    Statement s = ResourceFactory.createStatement(talha, take, javaProgramming);
    model.add(s); // add the statement (triple) to the model
    printModel(model);
}

Here's the results I got:

------------------
| name | surname |
==================
------------------

Finally my sample ontology:

]>

Joshua Taylor · Accepted Answer

This answer is also at the duplicate on answers.semanticweb.com.

Your query is asking for a triple in which the object is the literal "JavaProgramming", but the code Resource javaProgramming = model.createResource(baseUri + "JavaProgramming"); creates a resource. You need to query for the resource rather than a string. The model that you create, aside from the ontology code, is this (notice that we see :JavaProgramming, and not "JavaProgramming"):

@prefix :       .

:JavaProgramming  :bookGenre  "1" ;
        :bookId       "1" ;
        :bookName     "Java Programming" ;
        :bookRating   "3" ;
        :isbn         "121321312" ;
        :pageCount    "200" ;
        :publisherId  "1" .

:Talha  :age       "23" ;
        :gender    "1" ;
        :name      "Talha" ;
        :password  "00" ;
        :surname   "Kabakuş" ;
        :take      :JavaProgramming ;
        :userId    "1" ;
        :username  "talhak" .

On this data, you can run the following query (with :JavaProgramming) and get the following results.

prefix :      

select ?student ?name ?surname where {
  ?student :take :JavaProgramming ;
           :name ?name ;
           :surname ?surname .
}

---------------------------------
| student | name    | surname   |
=================================
| :Talha  | "Talha" | "Kabakuş" |
---------------------------------

Unable to retrieve results from owl using Jena

Answers (2)

Related Questions