code: public String getId(OWLClass entity) {
      for (OWLAnnotationProperty owlObjectProperty : ontology.getAnnotationPropertiesInSignature()) {
        if (ifExistsAnnotation(owlObjectProperty.toString(), "id")) {
          Set<String> annotation = getAnnotation(entity, owlObjectProperty.getIRI().toString());
          if (!annotation.isEmpty()) {
            return annotation.iterator().next();
          }
        }
      }
      return StringUtils.EMPTY;
    }
docs: TODO: what if the ontology terms have multiple IDs?