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Re: Semantic Web issues

From: Sandro Hawke <sandro@w3.org>
Date: Sat, 19 Jul 2003 12:08:27 -0400
Message-Id: <200307191608.h6JG8RWK026189@roke.hawke.org>
To: Drew McDermott <drew.mcdermott@yale.edu>
cc: abcharl@keyworld.net, www-rdf-logic@w3.org

>    Reasoning in the Semantic Web is monotonic and makes an open world
>    assumption, rather than nonmonotonic and making a closed world assumption.
> Why is SW reasoning monotonic and open-worldish?  Who will enforce
> these constraints?

I think people are using these terms almost as buzzwords to remind
folks that some common kinds of reasoning (as in Prolog: closed world,
unique names, non-mon) do not allow ad hoc composibility.  I'd say a
basic goal for the SemWeb is that agents be able to merge knowledge
from multiple sources with relative ease, and as far as I can tell,
that means using monotonic reasoning with no CWA or UNA.    

But there is certainly a place for explicitely closed worlds.  One
example I often hear is that if something isn't listed on
http://www.w3.org/TR then it is *not* a W3C Tech Report.   This gets
us near what I think people want to do with nonmon and CWA.  I've
written rule bases which say things like "someone is absent from a
meeting if the published records of that meeting do not show them
present."   I think that's fine.

So "who will enforce these contraints?"  Users who want useful and
reliable (true when it matters) results.  Some tempting designs may
give badly wrong answers when KBs from around the web are merged, or
extracts from some KB are cached or republished.  (Your approach to
encoding FOL into RDF had this problem, since an extract of the RDF
graph had quite different (possibly opposite) propositional content
from the original graph.  Of course this didn't matter as long as the
data never escaped the lab to be turned into frankendata.)

> I think people tend to overreact to the possibility of inconsistency.
> They're visualizing smoke coming out of their laptops, as it does on
> Star Trek.


On the other hand, software fed data not in line with its design
generally does behave quite poorly.

    -- sandro
Received on Saturday, 19 July 2003 12:08:36 UTC

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