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Re: Notes on updates to RDF Schema

From: Frank Manola <fmanola@mitre.org>
Date: Thu, 31 Oct 2002 11:12:03 -0500
Message-ID: <3DC15653.9050403@mitre.org>
To: Brian McBride <bwm@hplb.hpl.hp.com>
CC: Patrick Stickler <patrick.stickler@nokia.com>, ext pat hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org

Brian McBride wrote:

> At 08:53 31/10/2002 -0500, Frank Manola wrote:
> 
>> The RDF normative specs may or may not define literals as resources, 
>> but if they do, they better not do it by saying:
>>
>> >>>
>> >>>   rdfs:Literal rdfs:subClassOf rdfs:Resource .
>> >>>
>>
>> because classes (including Literal and Resource) and subclasses are 
>> not defined in RDF, they are defined in RDFS (note the namespace 
>> prefix). M&S said literals and resources were disjoint, but didn't do 
>> it using declarations involving classes.
> 
> 
> Where?


I was interpreting the material at the beginning of Section 5 of M&S 
(just above figure 11) as meaning they were disjoint:

 
"The RDF data model is defined formally as follows:

   1. There is a set called Resources.
   2. There is a set called Literals.
   3. There is a subset of Resources called Properties.
   4. There is a set called Statements, each element of which is a triple of the form

      {pred, sub, obj}

      Where pred is a property (member of Properties), sub is a resource 

      (member of Resources), and obj is either a resource or a literal (member of Literals)"


On reading this again, I can see there's some wiggle-room for the 
lawyers, in that there is no explicit statement that they are disjoint, 
so the sets could presumably intersect.  However,

1. Item #3 specifically indicates the set relationship between Resources 
and Properties, and there is no such indication that there is any 
relationship between Resources and Literals

2.  the last sentence does say "either a resource or a literal", and 
doesn't say "or both" (and yes I know about inclusive ORs).


Also, if they aren't disjoint, so there are literals that are also resources:

 

a.  how do I draw graphs with them?  Boxy ovals?
b.  how do I write them in RDF/XML?

<ex:prop rdf:mayberesource>ex:literalandresource</ex:prop>?

--Frank



-- 
Frank Manola                   The MITRE Corporation
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Received on Thursday, 31 October 2002 10:59:42 EST

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