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]

    You can use the asterisk (*)  wildcard character as part of a
    user identifier. For example, if you want to specify all users in
    a group, you can enter [system3, *] as the identifier.

    When Oracle Rdb creates a database, it automatically creates an
    ACL entry with the identifier [*,*] (also known as PUBLIC), which
    specifies the privileges given to all users on the system.

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