CODEWITHSUNDEEP
javajenaontologydbpediatdb
sergi123
sergi123

Reputation: 189

Jena TDB: Querying a named model

I'm trying to query a Jena named model that I previously stored (precisely DBPedia TBox). Storage is done in the following way

Dataset dataset = TDBFactory.createDataset(path);
dataset.begin(ReadWrite.WRITE);
Model model = dataset.getNamedModel(graph);
OntModel ontModel = ModelFactory.createOntologyModel();
model.add(FileManager.get().readModel(ontModel, dbpedia));
model.commit();
model.close();
dataset.commit();
dataset.end();
dataset.close();

path contains the path to TDB, graph contains the name of the named model and dbpedia contains the path to the OWL file. Until this point everything seems fine:

When I later want to query the model, I do the following:

Dataset dataset = TDBFactory.createDataset(path);
dataset.begin(ReadWrite.READ);
List<String> out = Lists.newArrayList();
try(QueryExecution qExec = QueryExecutionFactory.create("SELECT * { GRAPH ?g {?s ?p ?o}}",  dataset.getNamedModel(graph))) {
    ResultSet rs = qExec.execSelect();
    ResultSetFormatter.out(rs);
    rs.forEachRemaining(triple -> out.add(triple.toString()));
} catch (Exception e) {
    e.printStackTrace();
}
dataset.close();

The output from ResultSetFormatter.out(rs) is empty, as follows:

-----------------
| s | p | o | g |
=================
-----------------

However, in debugger mode, I can clearly see that the property dataset from dataset.getNamedModel(graph) clearly has data there.

enter image description here

I assume then that my problem is the query, but that seems fine to me. Am I missing something?

Thanks!

Upvotes: 0

Views: 291

Answers (1)

AndyS
AndyS

Reputation: 16630

QueryExecutionFactory.create("SELECT * { GRAPH ?g {?s ?p ?o}}", dataset.getNamedModel(graph)))

That asks the query on the graph in isolation. Graphs do not have names - their slot in the dataset has the name.

Querying just a model is querying the default graph of the dataset (that gets created internally to make the query execution).

Try QueryExecutionFactory.create("SELECT * { GRAPH ?g {?s ?p ?o}}", dataset)

Upvotes: 1

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