W3C home > Mailing lists > Public > www-rdf-interest@w3.org > October 2001

Re: RDFCore Update

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 19 Oct 2001 22:57:41 -0400
To: tpassin@home.com
Cc: www-rdf-interest@w3.org
Message-Id: <20011019225741F.pfps@research.bell-labs.com>
From: "Thomas B. Passin" <tpassin@home.com>
Subject: Re: RDFCore Update
Date: Fri, 19 Oct 2001 21:12:28 -0400

[...]

> Hold on a minute, Peter, not so fast.  As I understand it, monotonocity
> means that if you add additional facts to the universe of interest, you do
> not contradict already established facts.  In this case, you have not added
> any inconsistency, so no non-monotonicity (gad, that's a terrible phrase -
> did I really write it?).  I agree that you could have done (Susan rdf:type
> Dog), but on the web, that is always going to be a real possibility anyway
> and has to be dealt with.

Not at all.  Monotonicity means that adding new stuff does not result in
fewer consequences, nor does it turn a contradiction into a
non-contradiction.  The new stuff can certainly contradict the old, in which
case you get --- wait for it --- a contradiction.

> Back to your example, say the processor finds your first statement first, it
> would either not try to type match (since it has no information) or it would
> infer that Susan must be a Person. This is akin to "lax" validation in XML
> Schema.   If later it discovers some other type information about Susan, the
> processor must check and see if there is an inconsistency or not.  Again,
> the possibility has to dealt with somehow.

> So I don't see why it is any different an issue that for any other
> assertions.  I do agree that this argument supports the descriptive view
> over the prescriptive view.

Agreed, data type information can be handled in just the same way as other
information.

> Now suppose that the type is an integral part of the label of a literal.
> The issue of knowing that Susan is a sister but not that Susan is a person
> doesn't arise (unless the literal value omits this fact), but the problem is
> just removed one step.  Somewhere that datatype has to be defined, we hope
> in RDF, and because order of evaluation is not specified - as you pointed
> out, right? -  who is to say that the processor would have discovered that
> type before it discovered Susan the sister?  And even if this were handled,
> there could still be an inconsistency between the type as defined and the
> type as used in the assertion about Susan.

If the complete type is an integral part of every literal then you are in
the situation where you have complete knowledge, and the descriptive and
prescriptive readings are the same.  (If you have other sources of typing
information then you can still get inconsistencies, of course.)  You can
define your formalism so that the type theory is built in a priori, and
thus, by definition, is available before everything else.  

Even if the type information comes from an external source, such as XML
Schema datatypes, you can arrange that RDF has to process type tags
attached to literals before the literal is processed.

However, all the above states is that it is possible to have complete type
information available, not that this would be a good thing for RDF.

> So it seems to me that every point you raised would be an equal objection
> for the other approaches that are being discussed.

I'm not sure what you are getting at here.  I'm just arguing against the
prescriptive reading, and am not arguing (here) for any data typeing
method.

> On the other hand, I am a fan of Conceptual  Graphs, and they do use the
> label block to specify the type.  But it is assumed that the processor has
> already sucked up the classification of types, which is not the case here,
> is it?

> Cheers,
> 
> Tom P

peter
Received on Friday, 19 October 2001 22:59:27 GMT

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