W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > July 2001

Re: rdfms-graph: Food for thought

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 23 Jul 2001 19:40:52 -0700
Message-Id: <v04210116b7828e27aa0e@[130.107.66.237]>
To: Graham Klyne <Graham.Klyne@Baltimore.com>
Cc: w3c-rdfcore-wg@w3.org
>At 08:16 PM 7/16/01 -0500, Aaron Swartz wrote:
>>On Monday, July 16, 2001, at 02:48  PM, Graham Klyne wrote:
>>
>>>E.g. when exchanging RDF between systems (the reason for 
>>>standardization), do we really want to specify that the existence 
>>>of a node, without properties, is significant?  If so, we must 
>>>define the significance, and that looks awkward to me.
>>
>>Can you explain why this seems awkward to you? It seems like a 
>>perfectly reasonable thing to do to me.
>>
>>The alternative seems to declare that:
>>
>><rdf:Description rdf:about="foo" />
>>
>>means:
>>
>><foo> rdf:type rdfs:Resource .
>>
>>which seems even more awkward.
>
>Actually, I think that is a relatively painless way of interpreting 
>nodes without properties (one that I hadn't thought of).
>
>The "awkwardness" to which I refer is:
>
>(a) how is one to represent such a node in N-triples?  Currently, 
>there's no obvious way (apart from what you suggest above).
>
>(b) having selected an N-triples representation, some kind of 
>semantics must be defined -- it seems rather pointless to take 
>special steps to define a form and then say it adds nothing to the 
>meaning.
>
>That said, I think your suggestion above quite neatly addresses both 
>concerns (assuming that semantics for any triple of the form:
>
>   <foo> rdf:type <bar> .
>
>must be defined).

Right; the obvious (I should know better than to say that) 
interpretation of a 'bare' name is that it says that a thing exists 
with that name, which is usually vacuous, so harmless. And this is 
what <foo> rdf:type rdfs:Resource seems to say as well, in a kind of 
reified way where having an rdf:type is like having the property of 
existing somewhere in the domain.  So the obvious (?) semantics for 
this would say that the extension of I(rdf:type) has to be a subset 
of Rx(2|R)  and that <x, y> is in EXT(I(rdf:type)) just when x is in 
the set y. This provides a general-purpose way to say that something 
is in a subset of the universe - provided of course that the subset 
in question has a name - and then the case in question has y being 
the universe itself (which is required to be the denotation of 
rdfs:Resource, I presume) , so the assertion just says that x exists, 
which is always true.

Pat

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Received on Monday, 23 July 2001 22:40:46 EDT

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