Penrose can be used to correlate identities from different realms.

If there is a common attributes between the realms, you can directly join the realms using the common attributes. For instance, Realm1 contains Name and SSN, Realm2 contains Email and SSN. With Penrose you can create a source for each realms and define a relationship Realm1.SSN = Realm2.SSN. The resulting mapping will contain Name and SSN from Realm1, and Email and SSN from Realm2 where these values belong to the same identity.

If there is no common attributes between the realms, you can manually create a new table as a hub to join the sources. You are, however, required to populate and maintain the content of this table. For instance, Realm1 contains Name and Email, Realm2 contains Username and SSN. You can create a new table T which contains Name and the corresponding Username. Then define two relationships: Realm1.Name = T.Name, and T.Username = Realm2.Username. The resulting mapping will contain Name and Email from Realm1, and Username and SSN from Realm2 where these values belong to the same identity.