Detecting change to session state

Question

Apex 4.0.2
Say I have a form page with a bunch of items. An On Load process populates them using SELECT...INTO. When the page is submitted, is there a way I can identify which page items have changed so they can be recorded in a database table. A generic solution instead of the brute-force way of duplicating all page items as hidden items and comparing values during processing.
When a page is run in debug mode, I see messages like Saving same value P1_FOO or when viewing session state using the Dev toolbar, there is a status column with Inserted or Updated so it would appear that the Apex engine does track changes to page items beteween the time they are rendered and processed.
Any ideas? Thanks

Answer 1

Tony & Jari - Yes, using collections would seem like the best option. It is not as difficult as I had imagined. Something like
apex_collection.create_or_truncate_collection('FORM_DATA');
for c1 in (select ... from apex_application_page_items
where application_id=:APP_ID and page_id=:APP_PAGE_ID and item_name in (...))
loop
  apex_collection.add_member('FORM_DATA',c1.item_name,v(c1.item_name));
end loop; can be used to populate the collection in a On Load process.
An After Submit process would compare v('item_name') to the corresponding value in the collection and do what it needs to do.
John - Thanks, that would work too I guess.
Thanks all