Data dictionary — metadata — system & object privileges — dictionary structure — ``user'' tables - ``all'' tables — ``dba'' tables — ``v$'' tables — frequently used tables — usage examples — exercises — using the dictionary in PL/SQL programs — optional exercise.
Introduction to Oracle.)
Figure 1 presents the two-level structure of the dictionary. At the
root of the tree is the dictionary table, that features two attributes: table_name and comments. The comment field presents an informal description of the corresponding dictionary table.
For instance, we can request information about the dictionary table:
SQL> SELECT comments 2 FROM dictionary WHERE table_name='DICTIONARY' 3 /and get:
Description of data dictionary tables and viewsAs an exercise, write a query to find out how many tables make up the data dictionary.
The second level of the dictionary is divided into four categories of
tables. ``User'' tables describe the objects you own. They are only accessible to you. ``All'' tables describe the objects of all the users, and are accessible to all the users. ``DBA'' tables contain information only relevant and accessible to database administrators. And last, ``V$'' tables reflect the internal state of the DBMS and are mainly useful to DBAs for performance audit and optimisation.
You should refer to Figure 1 for a list of commonly-used dictionary tables. Also, remember that you can obtain the schema of any table with the desc command1 (see Introduction to Oracle)