Updating views

Does anyone know what the situation is regarding the case where a view is set up to prevent a particular user or users from accessing particular columns in a table? - Can a row be update, subject to the rules to enforce a one-to-one mapping between rows in the view and the parent table? Can a row be inserted? If so, what values do the columns that the user cannot see get? Can you set the defaults? Can you alter the behaviour using something like a stored procedure or a trigger? Is there any way to run a stored procedure (or Informix's equivalent, if indeed there is one) at a higher privilege level than the actual user has? Thanks for any help. Tony Webster