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RE: designating datatypes

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 24 Feb 2003 16:17:56 -0600
Message-Id: <p05111b59ba8046fe5931@[10.0.100.86]>
To: <Patrick.Stickler@nokia.com>
Cc: w3c-rdfcore-wg@w3.org

>  > -----Original Message-----
>>  From: ext pat hayes [mailto:phayes@ai.uwf.edu]
>>  Sent: 21 February, 2003 20:09
>>  To: Dave Beckett
>>  Cc: w3c-rdfcore-wg@w3.org
>>  Subject: designating datatypes
>>
>>
>>
>>  Dave, you might be interested in a change Im proposing to the
>>  datatypes section in the semantics document, as follows, in response
>>  to a comment by Peter. It introduces the 'name' as an integral part
>>  of a datatype. This is a patch and if you can think of a better
>>  terminology and a pointer to a suitable spec I  would be delighted.
>>
>>  -Pat
>>
>>  ------
>>  3.4 Dattayped interpretations
>>
>>  A datatype is an entity named by a uriref and characterized by a set
>>  of character strings called lexical forms and a mapping from that set
>>  to a set of values. (The built-in datatype rdf:XMLLiteral,
>>  exceptionally, allows pairs in its lexical space.) Exactly how these
>>  sets and mapping are defined is a matter external to RDF.
>>
>>  Formally, we will describe a datatype d as a 4-tuple consisting of
>>
>>  1. A uriref called the name of d
>>
>>  2. A set of character strings called the lexical space of d
>>
>>  3. A set called the value space of d
>>
>>  4. A mapping L2V(d) from the lexical space of d to the value space of
>>  d, called the lexical-to-value mapping of d
>
>So you're telling me that
>
>    ex:foo daml:equivalentTo xsd:integer .
>
>is then semantically invalid,

No, its fine. The conditions don't say that you HAVE to use the name, 
only that it is there to be used if you want to be sure of getting 
that very datatype.

>  since the "name" in the formal
>definition of xsd:integer is *xsd:integer* and I can't say
>"10"^^ex:foo and given the above statement mean the same
>thing as "10"^^xsd:integer?!!!

No, you can say that. And then normal DAML reasoning ought to let you 
come to that conclusion, since it presumably should allow a reasoner 
to substitute names known to be 'equal'. But it is asking rather a 
lot of a DAML (or OWL) reasoner, to get inside RDF literal syntax, 
and I bet that some of them wouldn't be able to handle it, in fact.

>If so, then I am adamantly opposed to this change.
>
>I've yet to understand Peter's need for this change, even after
>a good deal of private interchange with him, and remain completely
>unconvinced that this is necessary.

Well, I tend to agree, but he is most adamant that he wants it, and 
it seems harmless to let him have what he wants. Nothing else breaks, 
as far as I can see.

>It seems to me to be in direct conflict with the very core of RDF,
>that URIs denote resources without any requirement that the URI
>be an inherent part of those resources in any way.

The trouble is that datatyping uses the datatype URIs in a special 
way: it needs them to be proper names, not just symbols that denote, 
like logical constants. Logical names can be reinterpreted 
differently, but proper names refer 'rigidly'. They need to have the 
same denotation in ALL D-interpretations. (What these conditions do 
is make this 'same in all D-interps' condition absolutely explicit 
instead of its being implicit in the statement of the interpretation 
mapping.)  And that does raise a legitimate concern about how one 
gets a particular thing (a dataytpe in this case) so firmly attached 
to a URI.  Ultimately I agree with you that this goes beyond our 
remit to solve, but having the thing say what it's 'official'  URI 
is, is just a kind of semantic handle for doing this. It doesn't stop 
you or anyone else using another URI to refer to the thing, just like 
you all call me "Pat" even though it says "Patrick John" on my birth 
certificate.

So is that OK, with that understanding that allowing an 'official' 
name does not exclude the use of other names?

Pat

>
>Pat, if you can, please justify this change to the WG (or at
>least me).
>
>Thanks,
>
>Patrick


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Received on Monday, 24 February 2003 17:18:08 EST

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