Question:

 How the BITMAP index is stored?.  Basically i want to know the way a bitmap index is stored inside Oracle.  I have the basic idea that the bitmap index will create a bitmap for each distinct value exist in the table and accordingly it will  have the start rowid and end rowid mapped to the bitmap index.

Answer:

Bitmap indexes are stored as an array of zero-and-one values, with one entry for each row.  Bitmaps are created by doing a full-table scan of the indexed table, and they are very slow for updates.  Here are tips on using bitmap indexes:

 http://www.dba-oracle.com/oracle_tips_bitmapped_indexes.htm