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Subject: RE: access control information (formerly... Strawman)
!!! I had almost introduced the concept of Horn Clauses a few days ago, but I figured it might be too obscure. I do think it is something we should explore when defining the policy language. However, coming to agreement on the standard set of primitive predicates will be a substantial rub! > -----Original Message----- > From: Polar Humenn [mailto:polar@syr.edu] > Sent: Tuesday, June 12, 2001 5:37 AM > To: bill parducci > Cc: 'xacml@lists.oasis-open.org' > Subject: Re: access control information (formerly... Strawman) > > > > You could go for a strictly logical approach, i.e. Prolog like Horn > Clauses. Then you have a semantics. You just have to standardize the > primative predicates. > > -Polar > > > On Mon, 11 Jun 2001, bill parducci wrote: > > > "Simon Y. Blackwell" wrote: > > > > > > The problem with "insufficient funds to access" is it requires an > > > understanding of the meaning of the constraint "balance > > $5,000". (Yes, I > > > know by policy example was not precisely in this form > ...). To avoid the > > > requirement that the policy engine actually understand > the semantics of the > > > constraint, I suppose it could return "balance < > ?required-amount" which > > > would only require programming the policy engine such > that it understood the > > > semantics of some finite set of operators. It still gets > pretty ugly though. > > > > ugly indeed. no matter which way you take this there are issues of > > 'ugliness'. on one hand you are faced with developing a library of > > discrete responses that could be virtually limitless in > number if they > > are to provide usable information to all known test cases. > on the other > > hand, as you point out, application specific responses are likely to > > require some sort of out-of-band (predefined) understanding of > > semantics, etc. to react properly to the message (otherwise > you are no > > better off receiving a detailed response vs. 'no. go away'.) > > > > perhaps the middle ground is the development of some generalized > > semantics based upon the content of the request. > > > > <winging it/> suppose a doc had <balance> as a field, your response > > above would be a valid message ("balance < > ?required-amount"). in other > > words, responses would be based upon some generic > expressions (<, >, <>, > > =, +/-, etc.) and are limited to those fields presented in > the request > > itself. of course a document could be submitted that is missing > > necessary information, in which case you would be stuck > responding with > > 'all necessary information not present' or some such, but > as mentioned > > above, it is hard to think of a scenario whereby a valid > requestor can > > be totally ignorant of the recipient's requirements and > still be able to > > act in any meaningful way to the response codes reagardless of their > > content. > > > > b > > >
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