[Odrl-version2] RE: ODRL-Version2 Digest, Vol 9, Issue 9

[Alapan Arnab]

> The second example, together with the first, highlights that we need to be
> careful with <or> and <xor>.  Notice that in the first example, you talk
> about an "or container", meaning inclusive-or.  (I'm assuming a staff member
> who is also a student and consults for Rolling Stone can copy a).  In the
> second example, you again talk about "or", but here mean an exclusive-or.
> (I'm assuming I can't both do unlimited printing and make a backup.)      
> 
I did not consider the case of <xor> vs <or> and I agree that it does
make sense to consider that application. In the example above, I had
meant an <xor> situation. In this case, it makes sense to have all three
logical operators, and interpret them as defined by traditional boolean
algebra.
> <A>
> Surely, the state of no_copies must be checked at the implementation level -
> i.e. at the DRM controller, the license is translated to:
> if ((no_copies < 5) || (no_copies >= 5)) then copy f; A smart compiler could
> condense this down to always true; but I would not expect such features from
> a DRM controller. From a DRM controller, it should check the state of
> no_copies and then allow copy f.
> 
> <V2>
> I think you're assuming that the value of no_copies is known at the time of
> the request.  If this is the case, then the naïve algorithm that I suggested
> should work just fine.  More generally, if we assume all possibly relevant
> facts are known at the time of evaluation, then I think the algorithm gives
> the intuitively correct answer.  But suppose the value of no_copies is not
> known.  Then I think a naïve DRM controller will not grant the permission,
> thus giving an intuitively incorrect response, because neither (no_copies <
> 5) nor (no_copies >= 5) individually evaluates to true.   

>From an implementation point of view, surely the value of no_copies is
known to the DRM controller (as it is a required function of a
controller to keep track of state), and if it is not known (maybe
because this is the first time the license has been used for example),
then a default value (0 in this case) should be used?

Alapan
-- 
Alapan Arnab
Data Networks Architecture (DNA) Laboratory
Department of Computer Science
University of Cape Town
Rondebosch, 7700
South Africa

Tel: +27 21 650 3127
Web: http://people.cs.uct.ac.za/~aarnab/
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