A `natural´ decomposition of multi-level relations

It is shown that the analysis of functional dependencies is useful when one wants to decompose a multilevel relation in a collection of single-level relations. The decomposition of a multilevel relation into a collection of fourth normal form (4NF) relations according to various functional dependencies is studied. These decompositions are compared to the decomposition algorithms in single-level relations proposed by the Sea View project and by S. Jajodia and R. Sandhu (IEEE Symp. on Security & Privacy, 1991). It appears that the first step of the decomposition algorithms is simply the normalization of the multilevel relation in 3NF (or in 4NF). The authors propose an analysis of functional dependencies that seem natural from a semantical point of view. A multilevel relation is decomposed into 4NF relations according to these functional dependencies, and it is then shown how to decompose these relations into single-level relations. It is thought this analysis provides a good solution to the polyinstantiation problem and that it would lead to correct definitions of update operations