CAST « Object Oriented « Oracle PL/SQL Tutorial

32.15.1.The CAST Function
32.15.2.The CAST function converts an object type (such as a VARRAY) into a common type that can be queried. Oracle 10g automatically converts the VARRAY without the CAST.
32.15.3.Transform a collection into a table and reference it in a SQL query.
32.15.4.Cast value to custom type
32.15.5.Use view to cast records in result set to a type