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Re: comment horrocks-01

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Thu, 3 Apr 2003 19:50:08 +0100
Message-ID: <16012.33376.632225.715250@merlin.horrocks.net>
To: Graham Klyne <GK@NineByNine.org>
Cc: pat hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org

On March 13, Graham Klyne writes:
> This made me think of something (maybe) related.  Is this a reasonable 
> inference rule to contemplate?:
>     _:foo rdfs:label "cat"@en
> implies
>     _:foo rdfs:label "chat"@fr

I don't thing so, particularly not if you are implying that there is
some significance to the cat-chat correspondence!


> ?
> One could imagine similar inferences regarding comments.
> #g
> --
> At 14:53 12/03/2003 -0600, pat hayes wrote:
> >I think we need to pay some attention to this. This request reflects an 
> >energetic exchange of views within Webont, and although it did not emerge 
> >as a consensual group comment, it clearly reflects a very deep issue for 
> >some potentially large user communities for RDF.
> >
> >The issue is that the only available syntactic form for adding comments to 
> >RDF involves making RDF assertions, since rdf:comment is a genuine RDF 
> >property, so all such triples have genuine entailments. This means, in 
> >particular, that changing a comment in an ontology changes the formal 
> >entailments made by that ontology, so is a genuine logical change to that 
> >ontology. Whether or not this should be considered a bug or a feature is 
> >controversial, but there is no doubt that to those for whom it is a 
> >problem, it is a very serious and basic problem, something very close to a 
> >fatal can't-live-with objection to RDF.
> >
> >It also means that one can set up inference chains which are probably not 
> >what any rational person would want to do, eg by defining an 
> >rdfs:subPropertyOf rdf:comment and then expecting to be able to use that 
> >to infer that something is an rdf:comment value. This distinction isn't 
> >particularly important (IMO) in RDF itself, but it becomes more trenchant 
> >in OWL, where quite subtle and indirect chains of reasoning could, in 
> >principle, allow one to draw unexpected  (and probably unintended) 
> >conclusions about an rdf:comment value, eg by virtue of there only being 
> >three comments in the graph, a cardinality constraint applying to a 
> >superproperty of rdf:comment and an assertion that rdf:comment was 
> >functional could produce an inconsistency, or maybe allow one to conclude 
> >that an invisible comment must exist even though it is not in the graph. 
> >(The ambiguity in what this would really mean illustrates one of the 
> >aspects which I think most bothers Ian and others, which is that this 
> >treatment of rdf:comment muddles the distinction between the logical 
> >content of an RDF graph and what might be called the syntactic decorations 
> >of it, and hence muddies the semantic clarity of the language by importing 
> >things - in the case, comment values - into the semantic domain which do 
> >not belong there. Personally I am happier in muddier semantic waters than 
> >Ian is, but I recognize that his views are widely shared.)
> >
> >We could address this in various ways (dark triples, anyone?), but all but 
> >one of them are too ambitious at this stage, probably. One thing we could 
> >do relatively easily is for the MT to declare that all interpretations 
> >make all assertions of rdf:comment true. This in effect would cancel the 
> >entailments which bother Ian. What this amounts to in practice is that all 
> >comments are trivially entailed, so one cannot use entailment as a guide 
> >to associating a comment with a graph; one has to appeal to a more 
> >directly syntactic criterion, such as actually being in the graph.
> >
> >On the other hand, this might bother some other users who would prefer to 
> >use entailment as a general RDF 'glue', even for such things as comments.
> >
> >An alternative point of view is that problems will only arise if people 
> >fiddle with the machinery (which is forbidden in OWL-DL in any case), and 
> >that Ian's worries about development of large ontologies can probably be 
> >handled by providing some extra-RDF way of associating developer comments 
> >with RDF graphs, eg by adding non-RDF XML markup. This is rather a 
> >brush-off attitude, however, particularly if we do not actually provide 
> >any hints as to how this might be done.
> >
> >Comments? Is there any other way to allow for 'genuine' comments in an RDF 
> >graph?
> >
> >Pat
> >--
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> -------------------
> Graham Klyne
> <GK@NineByNine.org>
> PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E
Received on Thursday, 3 April 2003 12:49:42 UTC

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