Differences between tab and dual in Oracle

ViewCodeIt is found that there is a tab in the code, which serves almost the same purpose as dual, so I want to know the difference between the two. The information is as follows:

 

Tab is a view, as seen:

Create or replace view SYS. tab
Select O. Name,
Decode (O. Type #, 2, 'table', 3, 'cluster ',
4, 'view', 5, 'synonym'), T. Tab #
From SYS. Tab $ T, SYS. OBJ $ o
Where o. Owner # = userenv ('schemaid ')
And O. Type #> = 2
And O. Type # <= 5
And O. linkname is null
And O. OBJ # = T. OBJ #()

Dual is a table with a unique column.
This column is a dummy varchar, that returns what you type.
That's why if you type select * from dual, the result will be 'x '.

 

References:

Http://en.allexperts.com/q/Oracle-1451/tab-dual-1.htm