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[xacml-comment] Target merging and matching

From
John Howard <>
Date
2002-07-23T14:02:04+00:00
ID
002801c23251$1cca3970$
Thread
[xacml-comment] Target merging and matching
Hi,

 

I am trying to understand how the Target is 
computed and how the computed Target is then matched.  It is difficult to 
understand the intentions of the spec when combining targets.  Is it that 
the rules must have similar Targets if an overall Target is to be 
computed.

 

The issue can be summed up in the following 
example.

 

I have a rule set of two rules.  One applies 
to a subject with the role Nurse, the other applies to a subject with the 
role Doctor.  So I have:

 

RuleSet

    Rule (Rule1)

        
Target

        
    Subjects

        
        role=nurse

 

    Rule (Rule2)

        
Target

        
    Subjects

        
        role=doctor

 

If this is legal then there would be an overall 
target of:

 

Target

    Subjects

        
role=nurse

    
Subjects
        
role=doctor

 

The question now is how do I match this 
target.  There as been some discussion around the fact that multiple 
Subjects should be ANDed, this clearly does not work here.  One possibility 
is to OR when referring to the same attribute.  That would work here but 
not if Rule2 had a second Subject.  e.g.

 

    Rule (Rule2)

        
Target

        
    Subjects

        
        role=doctor

        
    
Subjects
                
otherAttr=otherValue

 

If this is legal then there would be 
an overall target of:

 

Target

    Subjects

        
role=nurse

    
Subjects
        
role=doctor

    
Subjects
        otherAttr=otherValue
 

This obviously is impossible to match 
against.  Is this a problem of having rules with differing targets, if it 
is then I can live with that.  It is a bit inflexible and it seems to 
suggest the overall target computing does not give a big advantage in processing 
time.  The alternative would appear to be to offer a list 
of Subjects, or something similar, so multiple targets could be 
generated and evaluated.  e.g.

 

Target

    Subjects

        Subject

        
    role=nurse

    Subjects

        Subject
    
        role=doctor

        
Subject
        
    otherAttr=otherValue

 

John 
Howard.
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