Rob Vesse created JENA-908:
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Summary: Turtle output can be empty when graph contains cyclic
blank node references
Key: JENA-908
URL: https://issues.apache.org/jira/browse/JENA-908
Project: Apache Jena
Issue Type: Bug
Components: RIOT
Affects Versions: Jena 2.13.0
Reporter: Rob Vesse
Assignee: Andy Seaborne
Priority: Critical
Discovered a bug in writing Turtle with the latest release, haven't checked
whether it applies to past versions of ARQ.
Simple test case using test data from the DAWG tests:
{noformat}
@Test
public void bnode_cycles() {
Model m =
RDFDataMgr.loadModel("testing/DAWG-Final/construct/data-ident.ttl");
Assert.assertTrue(m.size() > 0);
ByteArrayOutputStream output = new ByteArrayOutputStream();
RDFDataMgr.write(output, m, Lang.TURTLE);
ByteArrayInputStream input = new
ByteArrayInputStream(output.toByteArray());
System.out.println(new String(output.toByteArray(),
Charset.forName("utf-8")));
Model m2 = ModelFactory.createDefaultModel();
RDFDataMgr.read(m2, input, Lang.TURTLE);
Assert.assertTrue(m2.size() > 0);
Assert.assertTrue(m.isIsomorphicWith(m2));
}
{noformat}
Debugging this I can see that the problem appears to lie in {{TurtleShell}}
which refuses to write any triples because each subject appears as the object
of some other triple. This creates a cycle resulting in no data being output.
{{TurtleShell}} needs to detect and arbitrarily break the cycles such that it
can output the data successfully.
I'll commit this as a disabled test case in {{TestLangTurtle}} to make it easy
to start debugging.
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