Subject: Re: [Simple] xcap/geopriv alignment issue 8: exceptions

From: Ben Campbell <[email-masked]>
Date: Mon, 01 Dec 2003 10:19:57 -0600

Robert Sparks wrote:

> On Wed, 2003-11-26 at 08:31, Ben Campbell wrote:
> 
>>Robert Sparks wrote:
>>
>>
>>>(speaking from the floor)
>>>
>>>In the presence/IM systems I've been using on a daily basis for
>>>some time now, I do not have a way to say "Allow everybody in
>>>foo.com except bar" and I still find these systems useful.
>>
>>I do have to point out that most of the existing, big commercially 
>>deployed systems, are single-domain, non-interoperable systems. We make 
>>due with them because that is what exists. I did not think that is what 
>>we are trying to build here.
> 
> 
> No, but the question starting this thread is whether or not it would
> be acceptable to have a base authorization system that didn't support
> exceptions. My point is that there are environments where such a system
> would be useful. (And I don't think the single-domain/non-interoperable
> characteristics of the existing systems I refer to is pertainant to that
> statement.)
> 
> 
>>Let me back off from saying you cannot build a useful system without 
>>exceptions. Let me instead state that I have endured a number of 
>>customer requests for authorization models that cannot be implemented 
>>without exceptions.
> 
> 
> Is there something in this set of requests that would make having
> exceptions as an extension to the core protocol unacceptable?
> 

It really does not matter how it is structured, as long as we have the 
capability. For the scenarios I refer to, I think XCAP will not likely 
get significant use until exceptions are available.

> 
>>>On reflection, when using future systems I think I will prefer the model
>>>of explicitly listing those people I wish to authorize over excepting
>>>individuals from a set I cannot control and possibly cannot know.
>>>
>>>Thus, I don't think it is absolutely necessary to have that kind of
>>>statement in the initial xcap-auth mechanism.
>>>
>>
>>Out of curiosity, do you see it necessary to be able to say a rule 
>>applies to a domain at all? Or to generalize, to any "group" where 
>>membership is determined when the rule is applied, rather than when it 
>>is created?
> 
> 
> Useful. Useful enough that I want a system that supports the concept.
> But absolutely necessary? No. A core authorization system that did not
> support this concept would still be useful.

Certainly, there are scenarios for which exceptions are not needed to 
have a useful system. For that matter, there are scenarios where XCAP is 
not needed to have a useful system. This seems a specious argument, 
unless we are able to bound what scenarios are important to us.

> 
> 
>>>I do see the power of having such a statement to some applications
>>>that may consume presence, and I would very much like to have such
>>>a statement available. I think it is acceptable for this functionality
>>>to be an extension of the base xcap-auth tool.

I am not convinced that the cost of including a very simplistic 
exception mechanism (that is, no external resolution allowed for the 
exception clause) is that much of an incremental effort compared to the 
rest of the language. If we are talking about core plus extensions, I 
would prefer to see a limited exception clause in the core, and perhaps 
a more general one as an extension.

>>>
>>>RjS
>>>
>>>On Tue, 2003-11-25 at 15:07, Ben Campbell wrote:
>>>
>>>
>>>>>>So you have allowed John, Alice, Ben and Adam. That is _not_ 
>>>>>>the same as 
>>>>>>"Everyone but Bob". For example, what if Carol joins example.com 
>>>>>>tomorrow. The "Allow John, Alice, Ben, and Adam" rule will 
>>>>>>not include 
>>>>>>her, but the "Everyone but Bob rule" would.
>>>>>
>>>>>
>>>>>Then you add a permission statement for Carol. This works. Jonathan did not suggest throwing away exceptions indefinitely. He questioned the usability of the first cut of xcap-auth without exceptions, and my opinion is that it is usable in the manner I described.
>>>>>
>>>>
>>>>That assumes you know about Carol. My point is, these two cases are not 
>>>>the same thing. You might be able to simulate something like exceptions 
>>>>by doing this, if and only if you have full knowledge of the membership 
>>>>of example.com. I suspect that will commonly be false.
>>>>
>>>
>>>

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From: Ben Campbell <[email-masked]>
Date: Mon, 01 Dec 2003 10:19:57 -0600