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NotApplicable and combining algs

  • 1.  NotApplicable and combining algs

    Posted 08-26-2004 02:51
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    Subject: NotApplicable and combining algs


    
    Sections 7.10 and 7.11 of draft 13 say that in all cases, if no 
    elements provided to a combining algorithm apply then the combining 
    algorithm always returns NotApplicable. Is that really what we want? 
    Shouldn't I be free to write a combining algorithm, for example, that 
    returns Deny if no elements apply? I can think of many cases where this 
    would be very useful (at the top-level in a PDP and to replace 
    fall-through Deny rules).
    
    The reason I ask is twofold. First, I don't ever remember discussing 
    this issue, so I'm not sure if someone explicitly wanted to see this in 
    the spec or if it's just an oversight. Second, I think it breaks the 
    relationship shown on page 19, since it implies that before a combining 
    algorithm starts working with its elements, something above it will 
    already have checked applicability of all elements. I think it's clear 
    that we don't want that model. Basically, I think this is another case 
    where we should say that the combining algorithm decides, and it just 
    so happnes that all the standard algorithms return NotApplicable in 
    this case.
    
    Yes? No? What do people think? Again, maybe fodder for discussion 
    tomorrow?
    
    
    seth
    
    


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