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https://issues.apache.org/jira/browse/JENA-908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14390312#comment-14390312
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Andy Seaborne commented on JENA-908:
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While the last commit fixes the problem, the output is not as pretty as it
should be so there is still some work to do. It currently triples triples from
troublesome bnode cycles as flat triples, not predicate-object lists.
> 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
> Labels: BNodes, BlankNodes, Turtle
>
> 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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