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Re: [OWLWG-COMMENT] ISSUE-67 (reification): real semantic-free RDF-comments

From: Pat Hayes <phayes@ihmc.us>
Date: Thu, 29 Nov 2007 14:02:06 -0600
Message-Id: <p06230903c374ca2e1eda@[]>
To: Jeremy Carroll <jjc@hpl.hp.com>
Cc: Alan Ruttenberg <alanruttenberg@gmail.com>, Michael Schneider <schneid@fzi.de>, Owl Dev <public-owl-dev@w3.org>, Ian Horrocks <horrocks@cs.man.ac.uk>, bmotik@cs.man.ac.uk

>Rather than talk about universal role, i.e. an 
>object property; I perhaps should have talk 
>about a universal attribute, i.e. a data 
>property; or even the union of the two). In RDF, 
>since all literals are resources, a universal 
>role is a universal attribute.
>A worked example is given in:
>Briefly, to make RDF canonicalization work 
>effectively, I needed a source of meaningless 
>triples, that I could add or delete freely 
>without changing the semantics of the graph. For 
>simplicity I sufficed with a near-universal 
>attribute, with range xsd:long.

True isn't the same as meaningless.

>This can be achieved by defining the appropriate 
>semantics of a new property as a semantic 
>extension to RDF, or, less formally, with:
><rdf:RDF xml:base=²&c14n;² xmlns:c14n=²&c14n;#²>
>   <rdfs:Property rdf:ID=²true²>
>     <rdfs:description>This property is true whatever
>resource is its subject, and whatever literal is its object.
>Thus triples with literal objects, and c14n:true as
>predicate, can arbitrarily be added to and deleted from an RDF
>graph without changing its meaning. </rdfs:description>
>   </rdfs:Property>

Hmm. But it also means that any RDF graph 
*entails* the same graph with an arbitrary number 
of these triples added. So all graphs entail 
themselves with random "comments" attached in 
random "places". This does not seem like what one 
would want a reasoning engine to do, so how does 
one give a semantic justification for not 
allowing it?


>Or within OWL 1.0, with the defn
>class(rdfs:Resource complete
>       restriction(c14n:true cardinality=2^64))
>       dataValuedProperty( c14n:true range( xsd:long ) )
>In OWL 1.1, we have already had the universal role defined by:
>>    (A0) ClassAssertion(w owl:Thing)
>>    (A1) SubClassOf(owl:Thing ObjectHasValue(pA w))
>>    (A3) SubObjectPropertyOf(
>>           SubObjectPropertyChain(pA InverseObjectProperty(pA))
>>           pU )
>>    (A4) ObjectPropertyDomain(pU owl:Thing)
>>    (A5) ObjectPropertyRange(pU owl:Thing)
>A4 and A5 seem unnecessary
>The universal attribute cannot be defined 
>directly in OWL 1.1 DL, mapping this construct 
>to use DataProperty's hits various limits.
>The universal attribute can simply be defined by 
>fiat as the product of owl:Thing by rdfs:Literal 
>(mapped into the appropriate domain of 
>interpretation). Then it would be possible to 
>have every annotation property defined as having 
>such an extension. Then they would be explicitly 
>meaningless, in that knowing that such an 
>annotation held would tell you nothing.
>But consider an axiom that is legally 
>actionable: e.g. an axiom that contains within 
>one or more of:
>a) a libellous statement (e.g. classifying somebody within an offensive class)
>b) a culpably negligent proposition e.g.
>    subClassOf( owl:Thing, eg:KnownToBeSafeToConsume )
>   (which could well result in poisoning)
>Suppose that annotations are semantic free, then 
>for either of these axioms, attribution 
>information, such as who wrote them, can be 
>freely added or deleted, and the culpability 
>involved, would be ascribed mistakenly.
>Annotations have semantics. The question is what semantics.

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Received on Thursday, 29 November 2007 20:02:32 UTC

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