OASIS eXtensible Access Control Markup Language (XACML) TC

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10. Parameters for Combining Algorithms

  • 1.  10. Parameters for Combining Algorithms

    Posted 10-27-2003 17:59
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    Subject: 10. Parameters for Combining Algorithms


    This is an attempt to capture issues raised during the discussion
    of this item for future reference.  Note that the item has been
    closed for 2.0 in favor of solving the problem using XACML
    Extension Points (#11).
    
    Proposal: http://lists.oasis-open.org/archives/xacml/200305/msg00014.html
    
    1. Any new "paramters" element needs to be scoped so that it does
       not become a "kitchen sink" (used for arbitrary data and
       semantics that are difficult to control and reconcile with
       future versions of standard XACML).
    2. This changes the evaluation of combining algorithms: now
       sub-policies or rules must be evaluated in order to see if
       they contain parameters.  Previously, the combining algorithm
       did not depend on evaluation of sub-policies or rules.
    3. If parameters were limited to use with Rule Combining
       Algorithms, they would be easier to apply, since there are no
       references to external rules and all the rule content is local
       to the Policy document.
    4. Would need to define how to deal with missing paramters or a
       mismatch between parameters and the signature of the combining
       algorithm.
    5. If parameters are included in Policies, those Policies may be
       referenced from multiple PolicySets, each with its own
       combining algorithm.  Not all of the combining algorithms may
       expect the same parameters in the same order.
    6. Parameters could be added via a new XACML schema extension.
       Such an extension would not parse as valid XACML (since XACML
       does not define schema extension points).  This is not a
       problem because only PDPs that had been modified to understand
       the semantics of the new combining algorithms would be able to
       handle the new policies anyway - when a PDP was modified to
       handle the new combining algorithm, it could be modified to
       handle the new schema.
    7. The functionality of parameters used only for ordering or
       precedence can be handled by using one of the "ordered" forms
       of the standard combining algorithms and ordering the rules or
       policies as desired when composing the policy document.
    
    Anne
    -- 
    Anne H. Anderson             Email: Anne.Anderson@Sun.COM
    Sun Microsystems Laboratories
    1 Network Drive,UBUR02-311     Tel: 781/442-0928
    Burlington, MA 01803-0902 USA  Fax: 781/442-1692
    
    


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