As we all know how to create a table eg: create table emp (empno number(10), ename varchar2(25)). This sql statement creates a table with two columns(empno and ename), which contains all the important information regarding the employee. Similarly oracle database also contains SYSTEM tables which store data about the database itself (metadata). Here oracle builds a views on these tables to make it easier for sql to have a look at the content of the actual tables. To be precise views pacifies the access to the metadata. Oracle 10g contains two types of metadata views.

• Data dictionary views &
• Dynamic performance views.

Data dictionary views have the names begin with DBA_, ALL_ and USER_.

1. DBA_ : DBA_TABLES as an example shows all the tables present in the database.
2. ALL_ : ALL_TALBES shows all the tables of the user(created by himself) and other tables which are granted by the DBA.
3. USER_ : ALL_USER view shows all the tables created by the user only.

Most of the views that begin with V$ are called as dynamic performance views. Eg: V$Database, V$Version and V$Sql.

Note: As a DBA we are not supposed to manipulate metadata.