code: private Object getId(OWLClass oc) {
          if(oc.isAnonymous()) return null;
  
          String id = oc.toStringID();
  
          if(id.equals("<"+OWLImporter.THING_IRI+">") ||
                  id.equals(OWLImporter.THING_IRI)) {
              return NamedConcept.TOP;
          } else if(id.equals("<"+OWLImporter.NOTHING_IRI+">") ||
                  id.equals(OWLImporter.NOTHING_IRI)) {
              return NamedConcept.BOTTOM;
          } else {
              return id;
          }
      }
docs: Returns the identifier for an {@link OWLClass}. If the owl class is
  anonymous then it returns null.
  
  @param oc
  @return