private void setPrefixOfNamespace(String namespace, String value) {
   OWLModel owlModel = ontology.getOWLModel();
   try {
     owlModel.beginTransaction(
         "Change prefix of " + namespace + " to " + value, ontology.getName());
     owlModel.getNamespaceManager().setPrefix(namespace, value);
     owlModel.commitTransaction();
   } catch (Exception ex) {
     owlModel.rollbackTransaction();
     OWLUI.handleError(owlModel, ex);
   }
 }
 NamespaceManager getNamespaceManager() {
   return ontology.getOWLModel().getNamespaceManager();
 }