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Re: Monotony

From: Frank Manola <fmanola@mitre.org>
Date: Tue, 15 Oct 2002 20:42:35 -0400
Message-ID: <3DACB5FB.7020708@mitre.org>
To: pat hayes <phayes@ai.uwf.edu>
CC: seth@robustai.net, "www-rdf-comments@w3.org" <www-rdf-comments@w3.org>, "Patrick.Stickler@nokia.com" <Patrick.Stickler@nokia.com>


I agree with you.  My original statement shouldn't have said "when you 
have monotonicity and when you don't", but rather something like "when 
you want to deal with changes and when you don't".  The reference to 
database transactions was a reference to their use in providing a way of 
getting consistent results of queries (or consistent updates), in spite 
of the fact that the database is undergoing concurrent changes all the 
time.  The corresponding notion you'd need to use in the Web would need 
to be more relaxed in general (perhaps something on the order of the 
extended database transaction mechanisms people were looking at a lot in 
the 90's), but you still need to have some such notions (e.g., to 
account for the "states of belief" you mentioned).  Otherwise, how do 
you do your reasoning if the sets of axioms and facts are allowed to 
arbitrarily change during the reasoning process?


pat hayes wrote:

>> Frank Manola wrote:
>>> More to your
>>> original point, it seems to me what you want is the ability to control
>>> or specify when you have monotonicity and when you don't.  Kind of like
>>> a database transaction mechanism.
>> Exactly!   Whatever a  *logical* RDF graph is, it is certainly is a 
>> document or a cluster of documents - what it is *not* is the whole 
>> blody semantic web.  Yet we seem not to have any convention for RDF 
>> authors to state that simple fact about their RDF documents and 
>> clusters of documents.  But there are many ways that this can be 
>> implemented without breaking into any new specifications.  Well we 
>> might need to define some new properties, but nothing really major or 
>> tramatic.
> If we have ways of stating the boundaries of 
> documents/databases/whatever, and of referring to them (perhaps 
> implicitly) and saying explicitly that something follows from this 
> bounded thingie alone, then we could say a lot of things that we are 
> unable to say right now. And it wouldn't be rocket science to provide 
> for saying things like this. No argument there. But that is (or can be) 
> all monotonic. What is non-monotonic is using inference which makes 
> these 'closed-world' assumptions *without saying or recording that it 
> has made them*. And the reason why that isn't a good idea on the web (or 
> indeed in any large-scale communicative context, such as human society) 
> is that unless your listener shares your unspoken assumptions, they can 
> draw incorrect and unintended conclusions from what you tell them. That 
> is why non-monotonicity is dangerous.
> Of course people make mistakes, change their minds, correct their 
> mistakes, etc. BUt the fact that we use a vocabulary to talk about this 
> that talks of CHANGE is itself a tribute to the need to have a monotonic 
> underlying logic. If I tell you that Joe is a bird, you conclude that 
> Joe can fly, and I then tell you that Joe is a penguin, who made the 
> mistake? We might argue about this - I think you did, by assuming more 
> than I told you - but the nonmonotonic answer is, what mistake? There 
> never was a mistake. You concluded Joe could fly, now you conclude he 
> can't fly: so?. Nonmonotonic logic changes the logical rules to 
> accommodate to the current state of belief. Monotonic logic says, you 
> had to change your mind or you would now be inconsistent. I think that 
> like the rest of us you probably do actually think using a monotonic logic.
> Pat

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Tuesday, 15 October 2002 20:26:51 UTC

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