Oracle - Data Dictionary views Part - 1

There are dictionary views available after installing oracle data base that helps user to identify objects available on current data base.

USER_OBJECTS, ALL_OBJECTS, DBA_OBJECTS:
Gives information about various database objects owned by the current user, available to the current user, or all objects in the database, respectively.

USER_TABLES, ALL_TABLES, DBA_TABLES:
Displays information about tables owned by or available to the current user, respectively, or all tables in the Oracle database.

USER_INDEXES, ALL_INDEXES, DBA_INDEXES:
Displays information about indexes owned by or available to the current user, respectively, or all indexes in the Oracle database.

USER_VIEWS, ALL_VIEWS, DBA_VIEWS:
Displays information about views owned by or available to the current user, respectively, or all views in the Oracle database (including dictionary views).

USER_SEQUENCES, ALL_ SEQUENCES, DBA_ SEQUENCES:
Displays information about sequences owned by or available to the current user, respectively, or all sequences in the Oracle database.

USER_USERS, ALL_ USERS, DBA_ USERS:
Displays information about the current user, respectively, or all users in Oracle respectively.

USER_CONSTRAINTS, ALL_ CONSTRAINTS, DBA_ CONSTRAINTS:
Displays information about constraints owned by or available to the current user, respectively, or all constraints in the Oracle database.