Describe Oracle’s data dictionary.

What will be an ideal response?

The data dictionary in Oracle consists of tables and related views. The data dictionary gives
the structure and inside view of Oracle database, and it has grown with each Oracle
release. You can use SQL statements with data dictionary tables/views just like you would use
them with user tables/views. You can get information about various Oracle objects and users
of the database. The data dictionary contains static data dictionary views, which are owned
by user SYS. The static data dictionary views are based on tables that are updated with Oracle
DDL statements only. It should not be updated with DML statements. The SYS tables, views,
and synonyms are created with CATALOG.SQL script file. The procedural objects are created
with CATAPROC.SQL file. These scripts files are provided by Oracle and are copied into the
ORACLE\ORA92\RDBMS\ADMIN directory, along with other script files.
The script files also create public synonyms for data dictionary views. For example, synonym
tabs for user_tables and seq for user_sequences. Before displaying information from a view,
DESCRIBE its structure first to avoid unnecessary information.
There are additional views known as dynamic performance data dictionary views, or
simply V$ views. The V$ views are based on internal memory structures, or virtual tables, which begin with X$ prefix. The V$ views and X$ tables have information about the
instance. The information in the two data dictionary views is
? Static data dictionary views. These views are for information on database objects,
database data files, and database users. The views begin with USER_,
ALL_, DBA_, for example,
DBA_CONSTRAINTS, DBA_CONS_COLUMNS, DICTIONARY, DBA_INDEXES,
USER_TABLES, ALL_TRIGGERS, DBA_ROLES, DBA_PROFILES, DBA_SYS_PRIVS,
DBA_USERS, DBA_TABLESPACES, DBA_VIEWS, and so on.
? Dynamic performance data dictionary views. These views are for information on instance
objects, archive log files, and currently connected users, for example, V$SESSION,
V$PROCESS, V$TABLESPACE, V$SQL, V$SGA, and so on.