date format

hi,

how to change the default format for type date?
I have created a field on a table:

##
create table tbl_inventory (       item_id integer constraint c_pk primary key,    I.         purchase_date date,   II.
       fabrication_date date,  III.         expiration_date date
 
);
##

the error i got is: 

##
Database operation "dml" failed
(exception ERROR, "ERROR:  invalid input syntax for type date: "2008 7 22 {} {} {} {DD MONTH YYYY}"
")
##

I am concerned the input syntax for type date is YYYY-MM-DD. 
as default, postgresql is set to accept the format DD-MM-YYYY for type
date.

so far, i am not able to change the input format and so I need to change
the postgresql type date dafault format. 

best,
iuri