[OWLAPI-developer] Querying the rdfs:label properties of individuals

[Adam F. <a....@dc...>]

I have an input OWL file (here's an excerpt) that defines a class "noun"
and a bunch of instances, which have RDFS labels; I can load the file
into an OWLOntology and find all the OWLIndividuals that are members of
the class or its subclass (using a reasoner).

<owl:Class rdf:ID="noun">...</owl:Class>
...
<noun rdf:about="Asc#i_fr_m11">
  <rdfs:label xml:lang="fr">Production</rdfs:label>
  ...
</noun>

Now I need to "read" the values and xml:lang attributes of the RDFS
labels (for further processing).  The OWL API says that every property
is either a data or an object property (I've seen some other approaches
that distinguish RDF properties separately), so I expect the rdfs:label
to be a datatype property.  Is that right?


I've tried to get a rough start as follows:

URI rdfsLabelUri  = OWLRDFVocabulary.RDFS_LABEL.getURI();
OWLDataProperty rdfsLabelProperty =
   owlDataFactory.getOWLDataProperty(rdfsLabelUri);
...
private String getRdfsLabel(OWLIndividual x)
  throws OWLReasonerException {
  Set<OWLConstant> labels = inputReasoner.getRelatedValues(x,
        rdfsLabelProperty);
  if (labels.isEmpty()) {
    return null;
  }
  return labels.iterator().next().getLiteral();
}

but getRdfsLabel always returns null, even for individuals that I know
(by inspecting the input file) have rdfs:label values.  Have I got the
wrong end of the stick?