On the expressive power of the unary transformation model

Abstract

The Transformation Model (TRM) was recently introduced [10] in the literature by Sandhu and Ganta. TRM is based on the concept of transformation of rights. The propagation of access rights in TRM is authorized entirely by existing rights for the object in question. It has been demonstrated in the earlier work that TRM is useful for expressing various kinds of consistency, confidentiality, and integrity controls. In our previous work [10], a special case of TRM named Binary Transformation Model (BTRM) was defined. We proved that BTRM is equivalent in expressive power to TRM. This result indicates that it suffices to allow testing for only two cells of the matrix. In this paper we study the relationship between TRM and the Unary Transformation Model (UTRM). In UTRM, individual commands are restricted to testing for only one cell of the matrix (whereas individual TRM commands can test for multiple cells of the matrix). Contrary to our initial conjecture (of [10]), we found that TRM and UTRM are formally equivalent in terms of expressive power. The implications of this result on safety analysis is also discussed in this paper.