An associative array cannot be stored in the database.
A collection has only one dimension, but you can model a multidimensional collection by creating a collection whose elements are also collections.
You can pass composite variables to subprograms as a parameters.
To create a collection or record variable, you first define a collection or record type, and then you declare a variable of that type. A collection that is created in a PL/SQL block (with the syntax in Collection) is available only in that block.
The database stores the rows of a nested table in no particular order.
When you retrieve a nested table from the database into a PL/SQL variable, the rows are given consecutive subscripts starting at 1.