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.