Data Dictionary

• A collection, data dictionary,  is created and maintained by the Oracle server and contains information about the database.
  
• The basic structure is alike the other database data.
  
• Use SQL statement to access the data dictionary.(Read Only)
  
  Normarlly, users cannot access to the data dictionary table directly. They are only allowed to access to the view of the data dictionary.
  
  
  

What can a user find from the data dictionary :

1. Definitions of all schema objects in the database (tables, views, indexes, synonyms, sequences, precedures, functions, packages, triggers, and so on)
2. Default values for columns
3. Integrity constraint information
4. Names of Oracle users
5. Privileges and roles that each user has been granted
6. Other general database information