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Re: response to issue pfps-09

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 5 Feb 2003 11:21:32 -0600
Message-Id: <p05111b04ba66f5cd1bb3@[10.0.100.86]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: w3c-rdfcore-wg@w3.org

>From: pat hayes <phayes@ai.uwf.edu>
>Subject: response to issue pfps-09
>Date: Tue, 4 Feb 2003 17:49:00 -0600
>
>>  I believe that there is a missing part of datatypes in the RDF model
>>  theory, and, moreover, that this missing part makes datatypes unusable
>>  in RDF.  The missing part is a mechanism for tieing a URI reference to
>>  a datatype.
>>
>>  ----
>>
>>  The MT assumes that datatypes are defined externally to RDF, and that
>>  part of this defining process involves associating a uriref with each
>>  datatype which can be used as its 'name', ie the semantic assumption
>>  is that the denotation is defined externally.
>
>The MT provides mechanisms for communicating the lexical space, value
>space, and L2V map of these externally defined datatypes to datatyped
>interpretations.  However, it is lacking a mechanism for communicating the
>RDF ``name'' of the datatype to datatyped interpretations.

I think there are two issues here that I (we?) have been getting confused.

1. A D-interpretation should require that the denotation of a 
recognized datatype uriref is a particular datatype, as a semantic 
condition.

2. Some *mechanism* should be provided in the semantics document for 
assigning or attaching the denoted datatype to the datatype uriref.

I agree with 1, but have been arguing against 2. I thought you were 
arguing for 2, but I now suspect that you are in fact arguing for 1. 
It was my understanding that the current document actually specified 
1.  already, but on reading it carefully I see that it is implicit
(in the text: "Urirefs which denote recognized datatypes are required 
to have the same denotation in all D-interpretations, so recognizing 
a datatype amounts to fixing the meaning of a uriref. ") rather than 
explicit (in some equations), so I propose as a purely editorial 
change to make it explicit. To emphasize, this is not a change to the 
intended MT, only an editorial (expository) change to make the 
intended meaning clearer.

So if you were arguing for 1., then yes, and moreover that was always 
the intention, so I will try make this clearer, see below.  If 
however you wish to argue for 2 above, then we are in for a longer 
argument.


>  > I feel that this is
>>  entirely appropriate for a semantic specification, and that the
>>  general issue of how meanings can be associated with urirefs is
>>  beyond the scope of this WG.
>
>I disagree.  Datatyped interpretations need to know which uriref denotes a
>datatype. 
>
>In the absence of this connection in a datatyped interpretation, the only
>way to make datatyped interpretations useful in the model theory is to
>create semantic extensions that provide for the connection.  Thus any
>useful theory of datatypes will be a semantic extension of datatyped
>interpretations, just as RDFS is a semantic extension of RDF (but on a
>considerably smaller scale).
>
>>  A more practical answer to this comment is that the inference rules
>>  for datatypes each specify a certain kind of information about the
>>  datatype, and clearly state that the rule can be applied only when
>>  that kind of information is somehow made available to an inference
>>  engine. Since the use of urirefs as URLs which provide access to APIs
>>  is well established on the Web, this seems to provide an clear guide
>>  to implementers as to how to proceed.
>
>Sure, if I want to create a datatyped version of RDF, I know how to
>proceed.  I define my datatype, say octal integers <O,V,L2VO>, and say that my
>datatyped version of RDF has this datatype.  I also need a semantic
>constraint that says something like
>	IS(my:octal) = <O,V,L2VO>
>I thus have created not a form of D-interpretation, but a semantic
>extension of a D-interpretation.  Without this semantic extension, my
>datatype is useless, as there is no way of determining that
>	I("10"^^my:octal) = 8
>
>However, if RDF datatypes included information about their ``name'', and
>this was made part of D-interpretations, then I could just say that my
>datatype was <my:octal,O,V,L2VO> and then D-interpretations that included
>this datatype would have
>	I("10"^^my:octal) = 8
>without the need for any semantic extension.

Right, this was always the intention, that if ex:foo is a recognized 
datatype uriref, then there is some datatype x such that in any 
D-interpretation I , I(ex:foo) = x. I should make that more explicit, 
clearly.

Pat

>
>>  I therefore propose that the WG takes no action on the basis of this
>>  comment , except possibly to refer the issue to some other authority
>>  (eg the TAG group?)
>
>I would view this as a failure of the WG to provide usable datatypes.
>
>>  Pat
>
>Peter F. Patel-Schneider
>Bell Labs Research
>Lucent Technologies


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Received on Wednesday, 5 February 2003 12:19:50 EST

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