This is a text description of schema3.gif.  

This figure illustrates deallocating all unused space as described in the text. 
It shows a table, DQUON, before and after issuing the ALTER TABLE statement 
presented in the text.

Before, there are three extents of 10K, 20K, and 30K, respectively. After 
issuing the statement, there are two extents of 10K each.