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Re: Subclass of Thing/Resource

From: Tim Berners-Lee <timbl@w3.org>
Date: Fri, 3 Mar 2000 16:27:07 -0500
Message-ID: <018201bf8557$3a7a3640$84001d12@politburo.w3.org>
To: "Pierre-Antoine CHAMPIN" <champin@bat710.univ-lyon1.fr>
Cc: "ML RDF-interest" <www-rdf-interest@w3c.org>

I tim wrote:
>> 0. We could define (if starting from zero) define dc:creator to have
range
>> dc:person where
>> a person is the domain of properties dc:mailbox and sc:homepage and
>> dc:commonname.
>> That is the best solution.


Pierre-Antoine replied:

>do it, and people will write things like
>
><play:Person rdf:about="mailto:John@somewhere.org"/>
><play:Person rdf:about="http://www.somewhere.org/~Paul/">
><play:Person rdf:about="employee://somewhere.org/12345"/>
>
>et voila ! The above dc:creator statements are valid.


They are valid in as much as we do not have any mechanism in RDF
for causing a validity error. We can declare  that "play:mailbox" has a
domain of Person and a range of Mailbox, but we can't  yet say that People
and Mailboxes are mutually distinct.

>This is what makes RDF flexible enough to scale the web.


No, I don't think so.  Vagueness is NOT what RDF needs. It is the ability to
go in and annotate the relationship between two well-formed concepts from
different places.

For example, to say   the rdfs:domain of play:mailbox is dc:Person is a
useful link between schemata which can be written after play: and dc: have
been defined by others.
This is what allows RDF to scale as a well-defined web.

>> >URIs are ambiguous, yes, they have more than one interpretation level,
yes.
>>
>> No, no. We should be clean or no reasoning from all this will be
possible.
>> IMHO.
>
>My belief is that SOME reasoning will be possible,
>even if hard logic inference (with completeness and everything) will not.


It is entirely my intent that the platform will support hard logic
inference, with completeness
and everything.

>We won't prove theorems, no

Yes we will, this is entirely part of the idea. When you do ecommerce, you
have to be able to *prove* that you have completed a transaction.

> - but is there any universal truth among the web, anyway ?


There is no universal truth in the Semantic Web except for mathematics.
There will be sets of information which together form a consistent system.
i expect also there will be some very large corpuses of consistent data such
as the mass of catalogs and weather data and stock price information and so
on.

>> >We can't prevent people from using URI with different interpretations,

Yes we can and we must.  This is not going to be some sloppy HTML 2.0+-
excercise.
We can limit our procesing to to data we trust, and limit what we trust to
data whose semantics is well defined.

>> >so we'll have to use the context to tackle with it.
>>
>> we agree to differ then.
>
>well, I meant, we sure can ENCOURAGE people to use strict structures,
>and if they do, RDF agents will be able to perform very efficient and
powerful reasoning.
>but we can't rely on it - if navigator did rely only on HTML
recommendation, 3/4 of the web would be unreadable!


For a reasoning engine, 99.999% is unreadable.  That is whyc we need a
semantci web which is different: hard logic.

>one eroneous fact in a strict logical system can make the entire system
contradictory ;


A semantic web system always operates on a very small subset of the entire
system.
The SW engine will have to be always aware of where an RDF statement was
found,
whether in a document which is trusted (for what purpose?)  or in a logical
expression, for example.

>the web can not afford strict logic : its first axiom is "there is
contradiction".


No, the web must have strict logic, and each agent on the web must be able
in the end to exchange a proof of its conclusions based on classical
logic -- even if it used soft heuristics to find that proof.

>I'm thinking about writing a paper on the subject.
>I'll post it on the list.


I will be interested to read it.
My thoughts are mostly in linked around
http://wwww.w3.org/DesignIssues/Semantic

Tim

>  Pierre-Antoine
Received on Friday, 3 March 2000 16:27:11 GMT

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