How Does the Data Dictionary Work?

Each database has its own data dictionary that is stored in the SYSTEM tablespace and consists of two major parts :

1. The system- maintained group of base tables . The base tables are not normally accessed by users because the data is in a cryptic format.

2. The assorted collection of views that Oracle creates from the base tables. These are the views that users normally access.

Warning

Do not fiddle with the data dictionary tables. These tables are owned by the user SYS, and no one should alter them in any way. The database most likely will no longer work if they are changed, because Oracle uses the data dictionary to manage the database. (Oracle does provide a safe way to add tables and views, but we will not be discussing it here.)

Oracle uses the dictionary in this general fashion: Every time you ask for something ”whether a table, view, or row ”Oracle checks with the data dictionary to see if what you want exists and if you have rights to it. Then if you create, modify, or delete a table or view, Oracle updates the data dictionary with the new information. The data dictionary is a great reference tool .