Difference among Index by table, Nested table and Varray

Index by table	Nested table	Varray
1. This is unconstraint table	This is an unconstraint table	This is an constraint table
2. Not to store permanently In database table	To store permanently into database using SQL	To store permanently into database using SQL
3. We cannot add or remove Indexes	we can add or remove indexes using extend, trim collection Method	we can add or remove indexes using extend trim collection method
4.Exists, first, last, prior,Count, next, delete,Delete (element1, Element n)	Extend, trim, exists, first, last,prior, next, delete, count,delete (element1, element n)	Limit, extend, trim, exists,first, last, prior, next, count,delete
5. Indexes range from -ve to +ve	Indexes start with 1	Indexes starts with 1