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Subject: RE: [xacml] Issues Relating to Obligations

> 3. Another issue I am trying to remember is the question that current combining methods allow applicable policies and rules to be skipped if the value of the Effect can be determined without them. This means that some Obligations in applicable policies may not be discovered. This was debated extensively in the old days. (I am and was firmly in the optimized evaluation camp.) My recollection of the final resolution was that thru the proper choice of combining methods, it is possible to force all policies to be evaluated. Does anyone know if this is true? Bill or anybody else do you remember this debate and its outcome?


Yes, you can use combining algorithms to do this. If you have a policies with obligations for a permit decision for instance, you can use a deny-overrides algorithm to collect them all, since this will continue processing all policies even if it finds a permit decision. Conversely you can collect deny obligations with a permit-overrides.


I know that this might work but I don’t think it’s a good idea.

First, what if one wants to have a permit-overrides behavior for authorization decisions but collect all applicable obligations? The obligation- and authorization-combining behavior should be expressible separately and independent of each other.


An example use-case: consider a record containing psychology notes resulting from a couple counseling for Alice and Bob with doctor Charlie. Now suppose that Alice and Bob eventually break up and Alice wants to continue counseling with a second doctor Doris.

The overall policy is that the consent of either of the clients involved in the counseling is enough to grant access to the notes to a second psychologist (permit-overrides). On the other hand, Bob’s consent includes an obligation to redact his personally identifiable information (name and address) from the notes for any doctor other than his own psychologist. So, we need a permit-override behavior and yet we need to combine all the obligations.


Also, I think using the combing algorithms like that is essentially “tricking” the PDP to process the obligations in a certain way based on the side-effects of an authorization combining algorithm on obligations. I think it is not desirable to rely on a implications like that and it is better for the policy readability to rely on explicit parameters that tell the PDP how to process obligations and authorization decisions from the underlying elements.








Best regards,




> Hal



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