[BitBucket user: Alain Mazy]
[BitBucket date: 2017-06-21.09:15:22]

Dear Salim,

Thanks for the feedback.  I would translate that into 2 'software' requirements:

- we need a way to null tags instead of removing them
- for many UIDs, like the Frame Of Reference UID, we need to make sure we anonymize them the same way along all instances -> we should keep a map that will remember the anonymized UID of each source UID:

```
UID anonymize(UID& sourceUID) {
  // if this is the first time we encouter this sourceUID, generated a new UID and save it in a 'cache'

 // else, returned the cached UID
}
```
We'll need to define the lifetime of this 'cache'.  I would suggest that the cache is reset for each anonymization job.