The data dictionary is structured in tables and views, but it is also an important tool for all users, from end users to application designers and database administrators. You use SQL statements to access the data dictionary. Because the data dictionary is read-only, you can issue only queries against its tables and views.
The data dictionary has two columns. These columns are table_name and comments.
Example
select table_name , comments from dictionary;
select * from dictionary where table_name = ‘USER_OBJECTS’;
select * from dictionary where lower(comments) = ‘views’;