Multilevel Databases

In the context of multilevel security, every piece of information is associated with a classification level, and every user is associated with a clearance level. The classification and clearance levels are taken from the same set of security levels. This set is totally or partially ordered and forms a lattice. The ordering relation is called the dominance relation and is denoted by ³. An example of a totally ordered set is {Unclassified, Confidential, Secret} with Secret > Confidential > Unclassified. An example for a partially ordered set is {low, (Secret, NATO), (Secret, Defence), high} with (Secret, NATO) > low, (Secret, Defence) > low, high > (Secret, NATO), high > (Secret, Defence), (Secret, NATO) and (Secret, Defence) are incomparable.