Protecting Duplicate Entry in oracle Forms

Create a function
-----------------------------------
Function F_comparison (P1 varchar2, P2 varchar2)
Return number is
answer number :=0;
BEGIN
 IF P1 = P2 then
  answer := 1;
 END IF;
return(answer);
END;
----------------------
Create an item ctrl_item in control block and initialize this before validating with validate string(:block_name.item_name||:block_name.category||:block_name.color).
Then  Create a formula column (Match_found) in transaction block with formula F_comparison (:ctrl.ctrl_item, :block_name.item_name||:block_name.category||:block_name.color).
Then create a summary item in control block (Match_found) with the summary of (Match_found) transaction block.
At last create a validate trigger in transaction block

BEGIN
:ctrl.ctrl_item := :block_name.item_name||:block_name.category||:block_name.color;
IF :ctrl.Match_found > 1 then
   message('This Item is duplicated.');
   Raise form_trigger_failure ;
END IF;
END;