In the psbprint database, there are two related tables: “Users” and “Identifiers”.
Users is reasonably obvious, it contains most of the properties of a user (i.e. Location, email, Budget Centre, etc.)
Identifiers are, for want of a better description, something that can identify a user. The two most common types of identifiers are NetworkIDs and CardIDs. This means:
A user may have multiple identifiers. E.g. It’s common for a user to have both a NetworkID and a CardID. Also, It’s not unknown for a user to have multiple cards. Multiple network IDs is also possible.
Network IDs can exist without Card IDs. Card IDs can’t exist without network IDs. Well, they can, but without a Network ID, a Card ID is useless. Greatly simplifying, this is because when a Card ID is used for Secure release, Blueprint needs to match the Card ID to a network ID, so Blueprint can find all jobs that are owned by that network ID.
Thus Network IDs are “higher value” than Card IDs to Blueprint.
The root identifier is the highest value identifier that Blueprint has for a User. Usually, it is the first Network ID associated with a User.