Users with S and TS clearance will see all tuples in the Client relation. However, a user with C clearance will only see the first two tuples and a user with U clearance will see no tuples at all. Assume that a user with clearance C wishes to enter a tuple (CR74, David,Sinclaire) into the Client relation, where the primary key of the relation is clientNo. This insertion is disallowed because it violates the primary key constraint (see Section 3.2.5) for this relation. However, the inability to insert this new tuple informs the user with clearance C that a tuple exists with a primary key value of CR74 at a higher security class than
C. This compromises the security requirement that users should not be able to infer any information about objects that have a higher security classification