Using Oracle 9i Flashback Functionality
Author: James L. Colestock

Step 1: First you must configure Automatic Undo Management (AUM):  
            
This entails altering a few initialization parameters and creating the 
UNDO tablespace (if it does not already exist)

Add to the initSID.ora or SPFILE:
 
undo_management = AUTO

You must determine next the value of the undo_retention
parameter, which represents the amount of read consistency time,
in seconds, that shall be guaranteed - you will be able to
"flashback" atleast this far into the past.

If just converting to AUM you will have to simply set this 
figure per Oracle guidelines and refine later. For
database already in AUM, refer to V$UNDOSTAT. The specific 
undo_retention value as well as the size of undo tablespace to create
are determined using the following formulas:

Undo Segment Space Required = (undo_retention (secs) * max undo blocks per second * db_block_size)
(Example: 300 seconds * 50/blocks per sec * 8K = 120MB) 

Set undo_retention (seconds)in the initSID.ora or SPFILE:

undo_retention = XXX 
(Example: undo_retention = 7200; 2 hrs.)

Creating the Undo Tablespace:

SQL> create undo tablespace <name of your undo tablespace>
     datafile '/XX/oradata/undoXX.dbf' size <determined above>;

Set the Undo Tablespace in initSID.ora or SPFILE:

undo_tablespace = <name of your undo tablespace here>


 
Step 2:  Determine Time or SCN to "Flashback" to by Enabling Flashback and Searching for Data:

Work with the person who has lost the data 
toggling between flashback enabled and disabled using the DBMS_FLASHBACK
until you find the data you are looking for or determine that you cannot. There
is an ENABLE_AT_SYSTEM_CHANGE_NUMBER procedure as well
  
SQL>begin
     dbms_flashback.enable_at_time('15-JAN-03 11:49:00');  
    exception
   when others then
     dbms_output.put_line(sqlerrm);   
   end;   

SQL>begin
     dbms_flashback.disable;
    exception
     when others then
    dbms_output.put_line(sqlerrm);   
    end;


 
Step 3: Use Export and Import to Restore the Data  

# exp FLASHBACK_TIME='2003-01-15:12:05:00' TABLE=table_name USERID=source_user ROWS=Y file=dump_file_here

# imp USERID=user@SID file=dump_file_here