@Override
 public void writeExternal(ObjectOutput out) throws IOException {
   ODistributedVersionSerializer.INSTANCE.writeTo(out, this);
 }
 @Override
 public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
   ODistributedVersionSerializer.INSTANCE.readFrom(in, this);
 }
 @Override
 public String toString() {
   return ODistributedVersionSerializer.INSTANCE.toString(this);
 }