User identification

How are users identified in the system? The choices range from not at all to full identification that can be correlated by anybody to the user’s real-world identity.

We found the following implementation choices:

User is anonymous
The App does not identify its users
User has a single global pseudonym
The App identifies its users by pseudonym that is the same everywhere
User pseudonyms can be resolved by the systems operator
While other users only see user pseudonyms, the system operator knows the real-world identity of all users
User has a different pseudonym in each relationship
The App identifies its users by pseudonyms that are unique to a relationship
User is fully known
The App identifies its users by their real-world name