Good summary of collections

http://www.adp-gmbh.ch/ora/plsql/coll/index.html

associative arrays

1. think of them as hashes (like in perl)
2. the keys can be string or int which means they need to be unique. See http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14261/collections.htm#BABFACFA

nested tables

- no upper bound

varrays

-when declaring one, you'll need to define the upper bound