Error in PL/SQL documentation regarding multidimensional collections?

Question

Hi
This is a small issue, but I think the following, from PL/SQL reference 11.2 (http://docs.oracle.com/cd/E11882_01/appdev.112/e25519/composites.htm#BABIBDDG), is wrongly calling the data types (and the variables created of those types) nested tables.
Surely, anywhere you see "INDEX BY ..." it's an associative array. Hence, ntb1 is an associative array of associative arrays, and ntb2 is an associative array of varrays. Am I right?
Thanks,
Jason
Example 5–13 Nested Tables of Associative Arrays and Varrays of Strings
DECLARE
  TYPE tb1 IS TABLE OF INTEGER INDEX BY PLS_INTEGER; -- associative arrays
  v4 tb1;
  v5 tb1;
  TYPE ntb1 IS TABLE OF tb1 INDEX BY PLS_INTEGER; -- nested table of
  v2 ntb1; -- associative arrays
  TYPE va1 IS VARRAY(10) OF VARCHAR2(20); -- varray of strings
  v1 va1 := va1('hello', 'world');
  TYPE ntb2 IS TABLE OF va1 INDEX BY PLS_INTEGER; -- nested table of varrays
  v3 ntb2;
BEGIN
  v4(1) := 34; -- populate associative array
  v4(2) := 46456;
  v4(456) := 343;
  v2(23) := v4; -- populate nested table of associative arrays
  v3(34) := va1(33, 456, 656, 343); -- populate nested table of varrays
  v2(35) := v5; -- assign empty associative array to v2(35)
  v2(35)(2) := 78;
END;
/

Answer 1

>
This is a small issue, but I think the following, from PL/SQL reference 11.2 (http://docs.oracle.com/cd/E11882_01/appdev.112/e25519/composites.htm#BABIBDDG), is wrongly calling the data types (and the variables created of those types) nested tables.
Surely, anywhere you see "INDEX BY ..." it's an associative array. Hence, ntb1 is an associative array of associative arrays, and ntb2 is an associative array of varrays. Am I right?
>
Yes - the documentation is wrong on that point.
One of the key differences between an associative array and a nested table is how they are treated after creation if they have not yet been populated. The array is treated as EMPTY while the nested table is treated as UNITIALIZED.
The doc states this as well
>
Like a database table, an associative array:
Is empty (but not null) until you populate it
An uninitialized nested table variable is a null collection. You must initialize it, either by making it empty or by assigning a non-NULL value to it.
>
You can see that particular difference with this sample code.
DECLARE
  TYPE array_test1 IS table of VARCHAR2(15) index by PLS_INTEGER;
  my_array1 array_test1;
  TYPE nt_test1 IS TABLE OF VARCHAR2(15);  -- nested table type
  my_nt1 nt_test1; 
BEGIN
--  dbms_output.put_line('array 1 [' || my_array1(0) || '].');
  dbms_output.put_line('nt 1 [' || my_nt1(0) || '].');
END;The above will give this exception:
>
ORA-06531: Reference to uninitialized collection
ORA-06512: at line 11
>
If you 'uncomment' the first line and comment the second you will get a different exception:
>
ORA-01403: no data found
ORA-06512: at line 9