Oracle 9i Tutorial : Table and Data Dictionary

User Tables:

Are a collection of tables created and maintained by the user
Contain user information

Data Dictionary:

Is a collection of tables created and maintained by the Oracle Server

Contain database information

 Tables in the Oracle Database

User tables are tables created by the user, such as EMPLOYEES. There is another collection of tables and views in the Oracle database known as the data dictionary. This collection is created and maintained by the Oracle server and contains information about the database.
All data dictionary tables are owned by the SYS user. The base tables are rarely accessed by the user because the information in them is not easy to understand. Therefore, users typically access data dictionary views because the information is presented in a format that is easier to understand. Information stored in the data dictionary includes names of the Oracle server users, privileges granted to users, database object names, table constraints, and auditing information.

There are four categories of data dictionary views; each category has a distinct prefix that reflects its intended use.

Table and Data Dictionary

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