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Re: [OWL-S] arguments for PAI and PAC

From: David Martin <martin@AI.SRI.COM>
Date: Wed, 27 Aug 2003 12:56:32 -0700
Message-ID: <3F4D0CF0.5020202@ai.sri.com>
To: Jeff Lansing <jeff@polexis.com>
Cc: "'www-ws@w3.org'" <www-ws@w3.org>

Jeff Lansing wrote:

> David Martin wrote:
>> ...
>> We don't normally model a car as the set of its parts, because we've 
>> come to realize that it works better to use some other 
>> representational mechanism for the "part-of" relationship.
>> Similarly, we don't usually represent the class of, say, dogs, as the 
>> set of "life-traces" of individual dogs, or the class of humans as the 
>> set of "life-traces" of individual humans.  (Note that I'm not saying 
>> we should never do these things; just that we don't usually find it 
>> useful to do so.)
>> I suppose the obvious rejoinder might be: in modeling processes we are 
>> centrally concerned with behavior across time, so it *does* make sense 
>> to think of a process as a class of executions (which we most often 
>> call "execution traces" in our discussions).  And that thought is in 
>> the spirit that initially motivated us to model processes in this 
>> way.  But, at least in my view, experience has taught us that it's 
>> more natural to think of a process, and an execution of the process, 
>> as two different (though obviously very closely related) kinds of 
>> things, and model the relationships in some other way than class 
>> membership.
>> Again, I can't give any "proof" that processes-as-classes doesn't 
>> work.  I'm just making the pragmatic argument that it's too hard to 
>> work with.  We're building an ontology, and in my view, if an ontology 
>> doesn't reflect a natural way of thinking about a domain, it's not so 
>> likely to be used.
>> ...
> As I understand it, this is a several-thousand-year-old debate, so any 
> appeal to naturalness here can only be regarded with suspicion. 

Agreed.  But it seems to me there are very few examples of folks 
modeling a process as the set of its executions (certainly very few 
examples that have widespread use).  This may just be a lack of 
awareness on my part - if you know of good examples (widespread or not), 
please let me know.

> A lot of 
> people don't find abstract Forms to be so "natural", but that's 
> essentially what you're stuck with, when you separate processes from 
> sets of executions of processes.

I'm not sure what you mean by abstract Forms; could you elaborate a bit?

Thanks, David
Received on Wednesday, 27 August 2003 15:58:04 UTC

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