Up till now, a few secure models of object oriented databases have been proposed. Most of them support multilevel entities and more or less cover stories. In this paper, we undertake a more natural approach to model object oriented databases supporting multilevel entities which cope with the shortcomings of the previous models, viz the need of trusted mechanisms, the management of polyinstantiated objects and the inconsistency it may introduce in the database. The central idea is to decompose a multilevel object oriented database into a collection of single level databases. Hence, we split up the real universe into worlds corresponding to each security level. These worlds are the views of the universe by users at the corresponding levels, that was the reason of "MultiView" appellation. We present an animation of the MultiView model through creation, updating and consultation of objects. We show how we make use of cover stories without any specific problem. We also give a comparison with previous work and show how difficulties encountered in the earlier models can be avoided by the MultiView model.>

Data protection in a database involves inference controls which are sometimes of a semantic nature.The notion of neighborhood in a given context between two data is considered and a representation for context and neighborhood is proposed as well as a measurable definition for the neighborhood based on first order mathematical logic.

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.>