  Traditional database access control mechanisms use role based methods, with
generally row based and attribute based constraints for granularity, and
privacy is achieved mainly by using views. However if only a set of views
according to policy are made accessible to users, then this set should be
checked against the policy for the whole probable query history. The aim of
this work is to define a proactive decomposition algorithm according to the
attribute based policy rules and build a secure logical schema in which
relations are decomposed into several ones in order to inhibit joins or
inferences that may violate predefined privacy constraints. The attributes
whose association should not be inferred, are defined as having security
dependency among them and they form a new kind of context dependent attribute
based policy rule named as security dependent set. The decomposition algorithm
works on a logical schema with given security dependent sets and aims to
prohibit the inference of the association among the elements of these sets. It
is also proven that the decomposition technique generates a secure logical
schema that is in compliance with the given security dependent set constraints.
