W3C home > Mailing lists > Public > public-rdf-dawg-comments@w3.org > October 2007

Re: Issue with top-down and bottom-up semantics

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 31 Oct 2007 17:45:50 -0500
Message-Id: <p06230900c34eb3e391ad@[10.100.0.30]>
To: "Bob MacGregor" <bob.macgregor@gmail.com>
Cc: "Francis McCabe" <frankmccabe@mac.com>, public-rdf-dawg-comments@w3.org

>
>Your assumption that the Semantic Web is open world is unwarranted, i.e. does
>not stand up empirically.   Assuming that information is locally 
>complete is highly
>useful more often than not.  The open world assumption does seem to 
>be widely accepted
>among academic types, and makes for a nice sound bite, but we find in our
>own applications that negation-as-failure is highly useful, while 
>the open world
>assumption most of the time makes the logic less useful.  Although 
>its adoption is not
>mandatory in our implementation, we assume UNA and CWA in all of the 
>applications that I have seen.
>We also employ a variant of OWL that makes the same assumptions, and is
>therefore much more useful than standard OWL.

We all have been arguing about this for years, and I now think that 
everyone is right. The SWeb is globally open-world, no doubt, but it 
is chock full of locally-closed-world information sources, and often 
these are the ones that get used for practical work. We need both 
kinds of reasoning, and a methodology (which we don't have yet) for 
using them together without getting confused. The main problem, seems 
to me, is how to say in what respect (ie concerning what 'kind' of 
information or query) a given knowledge source is closed. I don't 
know how to talk about kinds of information. (Anyone have any ideas?)

As for UNA, I bet you aren't really using strict UNA, but a weaker 
form which might be called UNA-light: assume different names denote 
differently unless there a very good reason to conclude otherwise: 
and when that happens, fix it by substituting one name for the other 
so as to make UNA more likely next time. Something like that, am I 
right? Because others use that, and that seems to be a very good 
strategy to use even on the normal Web. Given two random URIs, the 
chances of them co-referring are vanishingly small; nevertheless, it 
does happen sometimes, and the costs of getting that wrong can be 
very high.

Pat
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Received on Wednesday, 31 October 2007 22:46:03 GMT

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