On the structural complexity of con ict of interest policies

We de ne a con ict of interest policy and show that the de nition is su ciently general to include several well-known generic policies as special cases and to articulate policies in di erent models of access control. We show that con ict of interest policies can be regarded as members of P(P(X)), for some set X, where P(X) denotes the powerset of X, and that such policies can be reduced to a canonical form. The set of canonical con ict of interest policies can be modelled by a subset of P(P(X)), A(P(X)). We derive upper and lower bounds for jA(P(X))j and for the maximum length of a string that would be required to describe a con ict of interest policy. We also discuss the composition of two con ict of interest policies, an ordering for con ict of interest policies, and possible simpli cations in the expression of such policies. The work of Jason Crampton is supported by EPSRC Award 98317878.