Consider an identifier πΌπ which appears several times in two datasets π΄ and π΅. After pseudonymisation, the identifier πΌπ is substituted with respect to one of the following policies:
Deterministic Pseudonymisation
πΌπ is universally replaced by the same pseudonym ππ ππ’ππ. It is consistent within a database and between different databases.
Document-randomised pseudonymisation
Each time πΌπ appears in a database, it is substituted with a different pseudonym (ππ ππ’ππ1, ππ ππ’ππ2,...). However, πΌπ is always mapped to the same collection of ( ππ ππ’ππ1, ππ ππ’ππ2) in the dataset π΄ and π΅.
Fully randomised pseudonymisation
For any occurrences of πΌπ within database π΄ or π΅, πΌπ is replaced by a different pseudonym (ππ ππ’ππ1, ππ ππ’ππ2,...).