Oracle Data Dictionary Structure

Oracle DBMS’s data dictionary is comprised of 2 types of objects:

1. Base Tables: Base Tables are the foundation of the Data Dictionary. It contains information about the database to which it is associated. It is READ-only, and only the Oracle server or processing engine can access it Users can’t access it. The data in that table are stored in normalized form and cryptic formats.
2. User Accessible Views: formatsThe data dictionary also contains views that are accessible to the user. It contains the information about base tables in a convenient way. They are extracted decoded versions of the Base table which contains useful information like user or table names. Generally, all users have access to this, unlike Base tables.

Both these tables and views are owned by SYS. No user should edit it as it can adversely affect the database.

In a Relational Database Management System (RDBMS), a data dictionary is a collection of READ-ONLY tables and views that contain metadata about the database. It typically contains data about all users in the system, their assigned roles and privileges, database objects, their structure, relationship, integrity constraints, default values and storage space details, auditing information, and many more. Since, it is READ-ONLY mode, only SELECT operation can be done on tables in the Data Dictionary.