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Re: Proposal to incorporate datatyping into the model theory (was Re: datatyping discussion)

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Tue, 23 Oct 2001 11:59:23 +0100
Message-Id: <5.1.0.14.2.20011023114258.039ba450@joy.songbird.com>
To: Pat Hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
At 06:14 PM 10/22/01 -0500, Pat Hayes wrote:
>Notice that the 'intended' reading is semantically anomalous since it 
>requires us to take the literal, er, literally, rather than interpreting 
>it in any way; it has a kind of use/mention glitch built into it. 
>(Admittedly this is kind of harmless for strings, since they do denote 
>themselves; that is why we are able to reinterpret rdf:value in the above 
>way as meaning equality, and get away with it.) Notice also that it makes 
>rdf:value seem kind of silly; if it means equality, and can only be used 
>with literals, why not just substitute the literal for the blank node and 
>get rid of the blank node? (Current answer: Because that would require us 
>to allow literals as subjects if we want to write the equivalent of _:1 
>rdf:type xsd:integer . Response: So, lets have literals as subjects, why 
>not? Or at any rate, let us face up to the fact that this prohibition is 
>purely an ad-hoc syntactic restriction imposed for no semantic reason.)

[...]

>I will work up a draft extension to the MT document  which covers it and 
>explains the alternatives, and then people can discuss it, how's that?

It sounds reasonable to me.  But there's one thing that still niggles me, 
and while I *think* it's covered in this proposal, I'm not totally 
sure.  It is the idea that the truth of a statement cannot be known without 
knowing the datatype of the literal it uses; e.g., DanC's example:

    ex:shoe shoe:size "10" .

I recall from the introduction to the current MT document the observation 
that the theory is concerned not so much with establishing truth or falsity 
for any given statement(s), but defining the conditions under which truth 
is preserved:

[[[
The chief utility of such a semantic theory is not to suggest
any particular processing model, or to provide any deep analysis of
the nature of the things being described by the language (in our
case, the nature of resources), but rather to provide a technical
tool to analyze the semantic properties of proposed operations on
the language; in particular, the extent to which they preserve
meaning.
]]]

Now, if I have knowledge (ex-RDF) that
     _:a shoe:size "10" .
and
     _:a shoe:size "10.0" .
are equivalent statements, then I can infer from the truth of the above 
example that
    ex:shoe shoe:size "10.0" .
is also true, without knowing that the literals used have a numeric data type.

You mentioned in another message the idea of a "default" datatype, in which 
literal strings denote themselves;  maybe the above issue is resolved by 
requiring that this default datatype be present in every 
interpretation?  Or:  any RDF that is true in some datatyped interpretation 
is also true in a corresponding interpretation with default datatyping.

#g


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Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
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Received on Tuesday, 23 October 2001 08:07:07 EDT

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