Nested categories for access control

We consider an access control hierarchy based on nested categories. Nested categories are sets of compartments with the property that any two categories are either disjoint or one wholly contains the other. We present a method for representing nested categories by assigning a pair of integers called k-values to each category. Authorization of a user to access an object is determined by comparing Ir-values of the user and object categories. Our method has the notable property that categories can be reorganized by computing new k-values for categories which are changed without affecting Ir-values of unchanged categories.