[Fwd: Useful change to XACML Schema]

Dear List

In the EC TAS3 project we have a requirement to be able to dynamically 
pass policies to PDPs, but the policies wont always be written in the 
XACML language. e.g. we have a behavioural trust engine where the policy 
language is written in SWI-Prolog. However we still want to use the 
XACML request response context to pass the policy. We believe that a 
simple addition of a new extension point to the PolicySet element will 
allow alternative Policy formats to be included in the request. The way 
to accomplish this can by adding an extension point to the xs:choice 
element to allow any element in any Namespace to be added to the 
request. The Specification should then make clear that the extension 
point should only be used to define Policy related elements.

Modified PolicySet Schema:

<xs:complexType name="PolicySetType">
         <xs:sequence>
             <xs:element ref="xacml:Description" minOccurs="0"/>
             <xs:element ref="xacml:PolicySetDefaults" minOccurs="0"/>
             <xs:element ref="xacml:Target"/>
             <xs:choice minOccurs="0" maxOccurs="unbounded">
                 <xs:element ref="xacml:PolicySet"/>
                 <xs:element ref="xacml:Policy"/>
                 <xs:element ref="xacml:PolicySetIdReference"/>
                 <xs:element ref="xacml:PolicyIdReference"/>
                 <xs:element ref="xacml:CombinerParameters"/>
                 <xs:element ref="xacml:PolicyCombinerParameters"/>
                 <xs:element ref="xacml:PolicySetCombinerParameters"/>
      *           <!-- Extension Point for defining Authorisation
Policies in different namespaces -->
                 <xs:element ref="xs:any"/>*
             </xs:choice>
             <xs:element ref="xacml:Obligations" minOccurs="0"/>
         </xs:sequence>
         <xs:attribute name="PolicySetId" type="xs:anyURI" use="required"/>
         <xs:attribute name="Version" type="xacml:VersionType"
default="1.0"/>
         <xs:attribute name="PolicyCombiningAlgId" type="xs:anyURI"
use="required"/>
     </xs:complexType>

Regards

David

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David W. Chadwick, BSc PhD
Professor of Information Systems Security
The Computing Laboratory, University of Kent, Canterbury, CT2 7NF
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