ABSTRACT
Most multilevel relational databases use the mandatory access control mechanism that is based on the Bell-LaPadula model [98]. This model depends on the terms of the subjects and the objects. The object may be a relation, a tuple, or an attribute within a tuple. The subject is the active process that needs to access some objects. Every object can be associated with a classification level such as U (unclassified), C (confidential), S (secret), or TS (top secret). Every subject also is associated with a classification level (unclassified, confidential, secret, or top secret). Classification levels are partially ordered.
