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Re: relationship of rdfs:Literal to rdfs:Resource

From: Graham Klyne <GK@ninebynine.org>
Date: Sun, 14 Sep 2003 11:25:28 +0100
Message-Id: <5.1.0.14.2.20030914111644.00b84c10@127.0.0.1>
To: Garret Wilson <garret@globalmentor.com>, www-rdf-interest@w3.org

To understand this, you need to be clear about the distinction between a 
"literal" or a "URI reference", which are syntactic parts of an RDF graph, 
and the things they denote (in some interpretation), which are resources in 
the domain of discourse.

Syntactically, literals and URI references are distinct entities in an RDF 
graph, but they both denote things drawn from a set of resources.

So, any value (e.g., the number 10) which might be denoted by a literal 
(e.g. "10"^^xsd:integer) could also be denoted by a URI (e.g. I might 
define the URI ref http://www.ninebynine.org/2003/09/number#_10 to have the 
number 10 as its intended denotation), and while they remain syntactically 
distinct entities, in the interpretation intended by my hypothetical 
definition, (and the presumed definition of xsd:integer) they would denote 
the same number 10.

(NOTE:  I have used the abbreviation xsd:integer above to stand for the 
full URI reference for the XML schema datatype 'integer', for convenience 
and because I can't remember the full URI.)

In the case of plain literals (without a datatype), they are self 
denoting.  So we have strings that are both syntactic entities in an RDF 
graph, *and* resources in the domain of discourse.  This may seem strange 
in light of the stated need to be clear of the distinction, but is actually 
fine;  indeed, some of the key proofs concerning RDF (and logic in general) 
depend on this idea (cf. Herbrand domain, or Herbrand interpretation in the 
RDF semantcis [1]).

#g
--

[1] http://www.w3.org/TR/rdf-mt/#defherbinterp
At 21:37 13/09/03 -0700, Garret Wilson wrote:

>RDF Schema says that rdfs:Literal is a subclass of rdfs:Resource.
>
>1. Does that mean that all RDF literals are resources? For example, is the 
>string "5" below a resource?
>
><rdf:Description>
>         <example:amount>5</example:amount>
></rdf:Description>
>
>RDF Concepts and Abstract Syntax says that, "Anything represented by a 
>literal could also be represented by a URI...." This brings me back to a 
>variation of an earlier question I presented on this list:
>
>2. What URI would I use to represent the literal "5" above, when referring 
>to the actual string of characters "5" (that is, not the value five)?
>
>3. What URI would I use to represent the xsd:boolean value represented by 
>the lexical form "true"?
>
>I'm still trying to get a handle on all the ends and outs of literals.
>
>Thanks,
>
>Garret

------------
Graham Klyne
GK@NineByNine.org
Received on Sunday, 14 September 2003 06:55:39 GMT

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