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Re: snmpconf BCP re: policy layering



It seems to me that Steve has a useful point here.  There is something 
different between the relationships:
1) instance specific vs instance independent
2) mechanism specific vs mechanism independent

The later is clearly a "generalization" relationship, elements of an 
abstraction hierarchy.
The former is not.  instance independent is not (in my mind) an abstraction 
of instance dependent.  Even if we assume (which I think most of us do) 
that what we are talking about in (1) is the difference between 
descriptions of things designed to be instantiated as specific instances 
and descriptions of things in more general terms, the generalization is not 
a generalization of "instance".  It is actually the addition of other 
concepts like role or technology, not an abstraction.

So, while I do not think that instance specific is orthogonal to the 
abstraction hierarchy, it does not seem to me to be the same "kind" of 
notion as the abstraction hierarchy.

Yours,
Joel M. Halpern

PS: One of the argument Steve and I had privately was whether you could 
have instance specific information that was otherwise higher on the 
abstraction hierarchy.  While I have think that the co0ncept may be 
inapplicable at the top of the abstraction hierarchy, it does not seem to 
me to be theoretically impossible to apply it at some middle levels.  In 
particular, prohibiting such cases by design seems excessive.  Rather, I 
would think that we should talk about instance specific as a separate 
concept, which is currently only known to apply to mechanism and 
implementation specific constructs.


At 08:20 AM 6/19/01 -0400, Jon Saperia wrote:
> > Assuming that's what is meant, however, I don't think that should be a
> > characteristic of the mechanism-specific layer. The mechanism,
> > implementation, domain, and service layers provide *abstraction* as you
> > move through the layers. However, instance-independence provides
> > simplification by reducing the number of instances but it doesn't
> > provide abstraction.
>
>It is at the bottom of the 'abstraction' chain and is presented for
>completeness - it is part of the hierarchy. In a sense the lowest level 
>beyond
>which (at the present time) we can not abstract further. The dictionary uses
>for it's first definition of abstract,
>
>    1 a : disassociated from any specific instance <abstract entity>
>
>This is what was on my mind when I started this (now nearly two years ago).