Uniquely identifies each user on the system.

    The user identifier consists of the standard OpenVMS user
    identification code (UIC), a group name, and a member name (user
    name). The group name is optional. The user identifier can be
    in either numeric or alphanumeric format. The following are all
    valid user identifiers that could identify the same user:

       K_JONES
       [SYSTEM3, K_JONES]
       [341,311]

    When Oracle Rdb creates a database, it automatically creates an
    access privilege set entry with the PUBLIC identifier, which
    grants all privileges except DBCTRL to any user. In access
    privilege set databases, the only wildcard allowed is the PUBLIC
    identifier.

    You cannot use more than one user identifier in a multiple
    identifier.