code: @Nonnull
      public Optional<IRI> getDefaultDocumentIRI() {
          if (ontologyIRI.isPresent()) {
              if (versionIRI.isPresent()) {
                  return versionIRI;
              } else {
                  return ontologyIRI;
              }
          } else {
              return Optional.absent();
          }
      }
docs: Gets the IRI which is used as a default for the document that contain a
  representation of an ontology with this ID. This will be the version IRI
  if there is an ontology IRI and version IRI, else it will be the ontology
  IRI if there is an ontology IRI but no version IRI, else it will be
  {@code null} if there is no ontology IRI. See
  <a href="http://www.w3.org/TR/owl2-syntax/#Ontology_Documents">Ontology
  Documents</a> in the OWL 2 Structural Specification.
  
  @return An Optional of the IRI that can be used as a default for an
  ontology document containing an ontology as identified by this
  ontology ID. Returns the default IRI or an Optional.absent.