How I can query a model on Jena TDB given a name

Question

I have a question.

I am trying to load my RDF files on Jena TDB.

I have written this code:

public void store(){
    String directory = "C:\\tdb";
    String source = "C:\\file1.rdf";
    String source1 = "C:\\file2.rdf";
    Dataset dataset = openTDB(directory);
    Model tdb = loadModel(source, dataset);
    dataset.addNamedModel("File1", tdb);

    Model tdb1 = loadModel(source1, dataset);
    dataset.addNamedModel("File2", tdb1);

    queryTDB(tdb, dataset);
    queryTDB(tdb1, dataset);

    tdb.close();
    tdb1.close();
    dataset.close();
}

public Dataset openTDB(String directory) {
    // open TDB dataset
    Dataset dataset = TDBFactory.createDataset(directory);
    return dataset;
}

public Model loadModel(String source, Dataset dataset) {

    Model tdb = dataset.getDefaultModel();
    FileManager.get().readModel( tdb, source, "RDF/XML" );
    return tdb;
}

In particular, I have two files and I want to load these files on Jena TDB. I have read on Internet that I can add a name to my models using "addNamedModel". In doing so, in the code above, I added the names "File1" and "File2".

Now, I want to query this dataset and I'm trying to write this code:

public void queryTDB(Model tdb, Dataset dataset) {

    String queryStr = "SELECT * { ?s ?p ?o }";

    Query query = QueryFactory.create(queryStr);
    QueryExecution qexec = QueryExecutionFactory.create(query, tdb);
    /*Execute the Query*/
    ResultSet results = qexec.execSelect();
    ResultSetFormatter.out(results) ;
    qexec.close();
}

This code works, but I would like to know how I can get the query results only for the model named "File1" (or "File2"). In fact, with the query written so, I get the results of both models.

How I can realize it?

Answer 1

You're not using absolute IRIs to name you graphs, so I don't know offhand what your graph names will be. You can use a query like this to help find out what they are:

select * {
  graph ?g {  
    ?s ?p ?o
  }
}

Once you've done that, you can continue using the graph ?g { … } pattern, or use from named to specify a graph in your query:

select *
from named <name-of-graph>
{
  ?s ?p ?o
}

select * {
  graph <name-of-graph> {  
    ?s ?p ?o
  }
}

See 13.2 Specifying RDF Datasets and 13.3 Querying the Dataset for the full details and for more examples.