Role Compatibility

While most changes of the current role of a process are implicit with certain actions, processes can also actively change their current role. This is specially useful for short term administration tasks and for server programs, whose subprocesses have to act in several roles without changing their user ID.⁵ In both cases, the original role should not be regained.

• changerole$_{tn}$(p:process, r:role) := process p actively changes its current role to r at time n

The right to do so is called Role Compatibility: A process may change its current role r$_1$ to role r$_2$, if role r$_2$ is in the set of compatible roles of role r$_1$.

• comproles(r:role):set of roles := set of compatible roles for role t

$$\mathrm{changerole}_{tn}(\mathrm{p,r}) \Rightarrow\ r \in \mathrm{comproles}_{tn}(\mathrm{currentrole}_{tn}(\mathrm{p}))$$ (15)