W3C home > Mailing lists > Public > www-rdf-rules@w3.org > December 2003

RE: a simple question

From: Wagner, G.R. <G.R.Wagner@tm.tue.nl>
Date: Wed, 3 Dec 2003 20:55:26 +0100
Message-ID: <D0D13B0440FC1F4995BC4CD7F84A3A42164938@tmex2.campus.tue.nl>
To: "pat hayes" <phayes@ihmc.us>, "Drew McDermott" <drew.mcdermott@yale.edu>
Cc: <www-rdf-rules@w3.org>

> The fact that you can't think of a 
> closer airport doesn't usually qualify as a good 
> reason to conclude that there isn't one, unless 
> you also know for sure that you know all the 
> airport locations, so that if you don't know it, 
> then its not there. Like, for example, if you 
> have a  list of all the airports. If you make 
> this explicit, as you should, then you are back 
> doing 'heavy-duty' reasoning.

Making a "local" (or predicate-specific) completeness
assumption and then using NAF (which is in this case 
equivalent to classical negation) is not 'heavy-duty',
is it?

> If you want to 
> make random guesses and hope for the best then 
> you can of course work faster, but don't expect 
> others to believe in your conclusions. 
> Negation-as-failure is NOT a good general 
> reasoning strategy: 99.99% of the time it will 
> immediately produce childishly ludicrous 
> conclusions

Noone wants to make "random guesses" (please try to be 
less simplistically polemic). Of course, if you use
NAF childishly, you will obtain "childishly ludicrous 
conclusions", but that's not the point. Drawing inferences
on the basis of NAF also give you "checkable valid 
conclusions". Of course not valid according to classical
logic (which seems to be your ONE TRUE LOGIC recommended
by the Lord), but according to the nonmonotonic logic 
of stable models.

> It is of utility only in those very special 
> circumstances when you have some reason to be 
> confident that you are dealing with a 'complete' 
> source of information about some aspect of some 
> topic (like having a list of all the airports). 
> ... The industrial uses of Prolog-style rules all 
> are designed within controlled environments, 
> typically using databases, where such special 
> conditions can be assumed. But on the web, we 
> can't assume that we are living in such a 
> controlled environment. 

I don't think there will be many (at least not
business-critical) applications that use all "the web"
for drawing inferences. Rather, they will use certain 
well-defined collections of URIs referencing documents
and DBs/KBs, which may even be restricted to the corporate
Intranet in the case of many business applications. In all 
these cases there is a well-defined information/knowledge 
scope, which allows you to use NAF both for "implementing"
classical negation when dealing with complete information
and for default reasoning in a well-defined meaningful
way (according to well-understood domain heuristics). 

Domain experts don't make "random guesses" when they apply 
their heuristics to draw nonmonotonic inferences. But you
want to discourage/forbid them to use a web rule standard
to do this, right?  Why? 

Gerd Wagner
Received on Wednesday, 3 December 2003 14:55:28 UTC

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