When you create a database, Oracle Rdb defines, populates,
    and manipulates the system tables. As the user performs data
    definition operations on the database, Oracle Rdb reads and
    modifies the system tables to reflect those operations. You
    should not modify any of the Oracle Rdb system tables using data
    manipulation language, nor should you define any domains based on
    system table fields. However, you can use regular Oracle Rdb data
    manipulation statements to retrieve the contents of the system
    tables. This means that your program can determine the structure
    and characteristics of the database by retrieving the fields of
    the system tables. See the Example Help subtopic under System_
    Tables in this Help library for an example of querying system
    tables.