code: private Set<OWLEntity> getChangeSignature() {
          Set<OWLEntity> result = new HashSet<OWLEntity>();
          final OWLOntologyChangeDataVisitor<Set<OWLEntity>, RuntimeException> visitor = new OWLOntologyChangeDataVisitor<Set<OWLEntity>, RuntimeException>() {
              @Override
              public Set<OWLEntity> visit(AddAxiomData data) throws RuntimeException {
                  return data.getAxiom().getSignature();
              }
  
              @Override
              public Set<OWLEntity> visit(RemoveAxiomData data) throws RuntimeException {
                  return data.getAxiom().getSignature();
              }
  
              @Override
              public Set<OWLEntity> visit(AddOntologyAnnotationData data) throws RuntimeException {
                  return data.getAnnotation().getSignature();
              }
  
              @Override
              public Set<OWLEntity> visit(RemoveOntologyAnnotationData data) throws RuntimeException {
                  return data.getAnnotation().getSignature();
              }
  
              @Override
              public Set<OWLEntity> visit(SetOntologyIDData data) throws RuntimeException {
                  return Collections.emptySet();
              }
  
              @Override
              public Set<OWLEntity> visit(AddImportData data) throws RuntimeException {
                  return Collections.emptySet();
              }
  
              @Override
              public Set<OWLEntity> visit(RemoveImportData data) throws RuntimeException {
                  return Collections.emptySet();
              }
          };
  
          for(OWLOntologyChangeRecord record : changeRecords) {
              result.addAll(record.getData().accept(visitor));
          }
          return result;
      }
docs: Gets the signature in the set of change records in this list.
  @return The signature.