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Re: Syntax-level typing (was Re: A data typing proposal)

From: Frank Manola <fmanola@mitre.org>
Date: Fri, 16 Aug 2002 07:49:16 -0400
Message-ID: <3D5CE6BC.9090208@mitre.org>
To: Patrick.Stickler@nokia.com
CC: connolly@w3.org, melnik@db.stanford.edu, guha@guha.com, w3c-rdfcore-wg@w3.org

Patrick.Stickler@nokia.com wrote:

>  
>>-----Original Message-----
>>From: ext Dan Connolly [mailto:connolly@w3.org]
>>Sent: 15 August, 2002 22:24
>>To: Stickler Patrick (NRC/Tampere)
>>Cc: melnik@db.stanford.edu; R.V.Guha; w3c-rdfcore-wg@w3.org
>>Subject: RE: Syntax-level typing (was Re: A data typing proposal)
>>
>>
>>In my opinion, RDF literals have always had the
>>property that if they look the same, they denote
>>the same thing, and if they look different
>>(modulo a few things like &#65; vs A),
>>they denote different things.
>>
> 
> Well, I don't see how that bears out in practice, in RDF
> applications, which apply different interpretations to
> the same literal string based on content.
> 
> 
>>In my opinion, RDF has always had string literals and
>>XML infoitem literals.
>>
> 
> As I see it, literals in RDF were simply a way to capture
> raw data that would be interpreted and utilized by higher
> level applications, and has said *nothing* whatsoever about
> the meaning or global consistency of meaning of such literal
> strings. In fact, if you look at the examples in the original 
> specs, it is fairly evident, IMO, that "Ora Lassila" is meant 
> to denote the person, just as much as the blank node is meant to
> denote him. Of course, not having a MT it is hard to argue
> religiously about that, but I think that your view is not the
> most obvious or most widely held.
> 
> Yes, your applications have presumed that literals constitute 
> global constants, but that is not asserted by the majority of
> applications that I am aware of, nor IMO by 
> the RDF specifications.
> 


I think this reveals some of the problems you get into when you define a 
data model (as RDF is) without explicitly defining any operations, in 
this case, some kind of equality test on literals.  Of course, you 
(Patrick) are correct in saying "literals in RDF were simply a way to 
capture raw data that would be interpreted and utilized by higher level 
applications", but I also think Dan's right.  Certainly the natural 
assumption in my opinion is that, in RDF as it is (without datatypes), 
literals are of type string, and there is a "built-in" equality test by 
string comparison.  Of course, RDF applications know this, and hence 
they know how to deal with the results of a string comparison in 
determining whether <ex:age>10</ex:age> is equal to 
<ex:weight>10</ex:weight> (or whether to use that comparison at all), 
but that involves application semantics over and above what is currently 
built into RDF (just as RDF would determine that ex:age and ex:weight 
weren't the same property, and an application might know that they 
were).  What we are contemplating in the datatypes proposal is whether 
(and how) to change this situation.

--Frank



-- 
Frank Manola                   The MITRE Corporation
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Received on Friday, 16 August 2002 07:35:24 EDT

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