A Formal Framework for Single Level Decomposition of Multilevel Relations

In this paper, we consider multilevel relations in which security classi cations are assigned at the granularity of individual data elements. Usually these multilevel relations exist only at the logical level. In reality, a multilevel relation is decomposed into a collection of single level base relations which are then physically stored in a database, and a recovery algorithm is used to reconstruct the original multilevel relation. In this paper we formalize the relationship that exists between the decomposition-independent ltered relations and the multilevel relations obtained from decomposed single level relations using the recovery algorithm. We state three requirements that must be met by any decomposition and recovery algorithms. In particular our algorithms in [7] meet these requirements.