  Crampton and Sellwood recently introduced a variant of relationship-based
access control based on the concepts of relationships, paths and principal
matching, to which we will refer as the RPPM model. In this paper, we show that
the RPPM model can be extended to provide support for caching of authorization
decisions and enforcement of separation of duty policies. We show that these
extensions are natural and powerful. Indeed, caching provides far greater
advantages in RPPM than it does in most other access control models and we are
able to support a wide range of separation of duty policies.
