why is this trigger not working

whenever i run this trigger in SQl Plus - nothing happens. I don't even get an indication that it failed to be created.

But is this trigger ok for Oracle

 CREATE OR REPLACE TRIGGER UpdateInstance FOR UPDATE ON Survey_Instance
AS

	DECLARE 	sp_Survey_instance_id int; 
	 	sp_Survey_instance_id = SELECT Survey_instance_id  FROM inserted;
	UPDATE 	Survey_Instance SET 	Survey_Instance.Update_datetime  =

                 END; Received on Wed Sep 18 2002 - 23:26:30 CEST