A formal framework for single level decomposition of multilevel relations

Multilevel relations in which security classifications are assigned at the granularity of individual data elements are considered. 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. The authors formalize the relationship that exists between the decomposition-independent filtered relations and the multilevel relations obtained from decomposed single level relations using the recovery algorithm. Three requirements that must be met by any decomposition and recovery algorithms are stated. It is pointed out that previous algorithms given by the authors (1990) meet these requirements