basic question on querying oracle tables in SAP ERP

Hi,

I have some basic question. This question is related to SAP ERP and Oracle Database. 

I can query the "dba_users" table....

***********

SQL> select username from dba_users where rownum < 2;

USERNAME

------------------------------

SYS

SQL>

******

But when I get all the tables, dba_users table is not found......

SQL> select tablespace_name, table_name from all_tables where table_name='dba_users';

no rows selected

SQL>

I am not sure why "all_tables" didn't return the "dba_users" table, though the "dba_users" table exists?

If you've any idea regarding this, can you please let us know.

Thanks,

Mahesh