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Re: rdfs:subClassOf and XSD derivation by restriction

From: Andreas Harth <andreas@harth.org>
Date: Sat, 3 Mar 2018 16:54:23 +0100
To: semantic-web@w3.org, Richard Smith <richard@ex-parrot.com>
Message-ID: <df932aef-dfb4-215f-b783-2204d2bdea8c@harth.org>
Hi Richard,

On 03/02/18 21:07, Richard Smith wrote:
> These are both datatypes in RDF, that is, we can say:
> 
> xsd:decimal a rdfs:Datatype . xsd:integer a rdfs:Datatype .

I think it helps to be clear about what entailment one assumes.

The above two statements are entailed under RDFS entailment recognising (at least) xsd:decimal and xsd:integer datatypes.

> Intuitively it seems like it ought to be, but I'm struggling to find
>  chapter and verse saying this is so.
> 
> The examples in 7.2.1 of RDF 1.1 Semantics tells us that any valid 
> statement of the form
> 
> ex:a ex:p "sss"^^xsd:decimal .
> 
> D-entails
> 
> ex:a ex:p "sss"^^xsd:integer .

The RDF 1.1 semantics spec gives that example and implicitely derives that entailment from the XSD specification (I think).

> And 2 of RDF Schema 1.1 says "If a class C is a subclass of a class 
> C', then all instances of C will also be instances of C'", but it 
> does not say the converse is true.  All instances of xsd:integer are 
> also instances of xsd:decimal, but can we say xsd:integer is a 
> subclass of xsd:decimal?

I haven't seen any formal definition on the level of RDF to that effect.

A similar case is the fact that the value spaces of the "primitive" datatypes are disjoint.
One could think of using owl:disjointWith to formalise that notion, e.g.,

xsd:float owl:disjointWith xsd:decimal .

But given that RDF, RDFS (and OWL) entailment is layered on top of D-entailment, datatypes have to be correctly handled even if the RDF processor does not know about RDF, RDFS and OWL entailment.
My hunch is that one would somehow implement the intented behaviour related to dataytpes, but, except for the entailments that are in the spec, outside the RDF, RDFS and OWL entailment machinery.

Cheers,
Andreas.
Received on Saturday, 3 March 2018 15:54:59 UTC

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