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Re: Show me the money - (was Subjects as Literals)

From: Nathan <nathan@webr3.org>
Date: Thu, 01 Jul 2010 21:18:58 +0100
Message-ID: <4C2CF832.3040002@webr3.org>
To: Antoine Zimmermann <antoine.zimmermann@deri.org>
CC: Jeremy Carroll <jeremy@topquadrant.com>, Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Antoine Zimmermann wrote:
> Jeremy, et al.,
> 
> 
> I think people are already showing the money but they do it 2 cents 
> after 2 cents ;-)  Here is my little 2 cent contribution.
> 
> To start with, I am on the side of the people in favour of allowing 
> literals in the subject position. I've read the discussion and pondered 
> the arguments on each side carefully, but I'm still convinced that it 
> would ultimately be the better option to allow them. I understand the 
> concern of those who would have to rework their architectures. Yet I 
> don't believe that the cost exceeds the benefits for those who are 
> starting to implement and for future implementations and future 
> developments of the standards.
> As Sandro said, RIF is using triples with literals as subjects, as 
> Robert Fuller said (in the LOD list), reasoners are internally inferring 
> triples with literals in subject position, and other use cases (more or 
> less convincing) have been proposed here. Why can't those inferences and 
> facts be exposed and published in an RDF document?
> 
> 
> Now I'd like to show some of the strange things that happen when you 
> combine SPARQL with inference regimes, that are due to the inability to 
> have literals (in the syntax) as subject.
> 
> 
> Assume that you have the following data, harvested from the Web:
> 
> :www dc:creator "Tim Berners-Lee" .
> :www dc:creator "Tim Berners-Lee"^^xsd:string .
> :www dc:creator :timbl .
> :timbl owl:sameAs "Tim Berners-Lee" .
> 
> 
> Note that literals are commonly used with dc:creator so this example is 
> fairly realistic.
> 
> Now, let us consider the following query:
> 
> SELECT ?x WHERE {
>    ?x a rdfs:Resource .
> }
> 
> under the RDFS-entailment regime, this would provide the following answer:
> ?x --> :timbl
> 
> Now, the following query:
> 
> SELECT ?y WHERE {
>    ?y a rdfs:Literal .
> }
> 
> would provide no answer (under RDFS-entailment) and:
> 
> SELECT ?z WHERE {
>    ?z a xsd:string .
> }
> 
> would provide no answer (under RDFS-entailment).
> 
> Now, imagine a SPARQL engine with an "RDFS+sameAs"-entailment regime. 
> The three queries above would give the following results:
> 
> ?x --> :timbl   // first query
> ?y --> :timbl   // second query (I can infer that :timbl is a rdfs:Literal)
> and the last would give nothing.
> 
> Now consider the query:
> 
> SELECT ?t WHERE {
>     ?u a rdfs:Literal .
>     ?u owl:sameAs ?t .
> }
> 
> It would give:
> 
> ?t --> "Tim Berners-Lee"
> ?t --> :timbl
> 
> However, the query:
> 
> SELECT ?u WHERE {
>     ?u a rdfs:Literal .
>     ?u owl:sameAs ?t .
> }
> 
> would give ?u -> :timbl .
> 
> 
> This is very weird for me.
> 

Something else that keeps coming up, a subset of owl always comes in to 
conversations, obviously owl:sameAs - there was a proposal from one Jim 
Hendler [1] at a RDF workshop thing to perhaps do something about moving 
these up a level to RDFS.

[1] http://www.w3.org/2009/12/rdf-ws/papers/ws31

Didn't seem to get much feedback or thoughts (afaik), but given the 
climate perhaps it's worth giving some strong consideration to as a 
community.

(Or just doing because it's a bloody good idea & would remove OWL from 
virtually every conversation we end up having).

ps: my only comment/addition to this was to add in Restriction's too

Best,

Nathan

forking again, sorry!
Received on Thursday, 1 July 2010 20:20:07 UTC

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