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Re: RDF Semantics: corrections(was: Re: RDF Semantics: two issues, connected to OWL)

From: Graham Klyne <GK@ninebynine.org>
Date: Tue, 06 Jan 2004 12:08:04 +0000
Message-Id: <5.1.0.14.2.20040106115510.025c4f78@127.0.0.1>
To: pat hayes <phayes@ihmc.us>
Cc: herman.ter.horst@philips.com, Sandro Hawke <sandro@w3.org>, www-rdf-comments@w3.org

At 16:35 05/01/04 -0800, pat hayes wrote:
>My understanding at present is that there is one outright error in the 
>document, an editing slip: the statement of the  RDFS entailment lemma in 
>appendix A should read the same as the one in the text:
>"rule lg" -> "rules lg, gl"
>with appropriate links, of course.
>
>The remaining comments from Herman are concerned with the way that 
>D-interpretations are defined.  After re-reading this correspondence I 
>think that the best way to proceed is to adopt Herman's suggested 
>rewording (with slight changes) for the RDFS semantic conditions.

On a quick read through, the revised text looks OK to me.

[...]

>PS to Herman: I am not so optimistic as you are about proving a version of 
>the entailment lemma for D-entailment. The issue here has always been that 
>datatypes are inherently idiosyncratic. For example, xsd:boolean has only 
>2 items in its value space, so for example the following is a valid 
>XSD-entailment:
>
>a p "true"^^xsd:boolean .
>a p "false"^^xsd:boolean .
>b type xsd:boolean .
>|-
>a p b .
>
>but I despair of writing a general set of rules which would be sensitive 
>to all possible value-space cardinality conditions. Similarly, there are 
>many valid XSD entailments arising from ordering constraints on particular 
>value spaces; and of course who knows what entailments might arise from 
>yet-to-be-defined datatypes? The real issue here is that the L2V(d)(x) 
>constraint is really arbitrarily powerful, even to the point of going 
>beyond first-order (ie R.E.) expressivity; and it is up to the particular 
>datatype how much of that power it chooses to wield: so I do not think 
>that we can possibly prove a general completeness lemma for datatype 
>entailment.

FWIW, I've done some work [1] to create an implementation of datatype-aware 
inferencing.  Of the two approaches that I've implemented, I rather like 
the one based on an idea noted in a paper by Pan/Horrocks [2], which 
generalizes the idea of Owl restrictions.  I've implemented a set of 
capabilities for xsd:integer that roughly mirror the capabilities provided 
by Cwm's builtin properties [3] (not yet including coercion and trig 
functions).

At the heart of this, in addition to the specification-defined attributes 
of a datatype, is a set of named relations associated with the datatype 
(e.g. members (a,b,c) of xsd_integer:sum satisfy a==b+c), which capture the 
idiosyncratic datatype properties.

#g
--

[1] http://www.ninebynine.org/RDFNotes/Swish/Intro.html

[2] Horrocks, I. and J. Pan, "Web Ontology Reasoning with Datatype Groups", 
2003.
     http://www.cs.man.ac.uk/~horrocks/Publications/download/2003/PaHo03a.pdf

[3] http://www.w3.org/2000/10/swap/doc/CwmBuiltins


------------
Graham Klyne
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Received on Tuesday, 6 January 2004 07:20:14 UTC

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