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Re: comment horrocks-01

From: Graham Klyne <GK@NineByNine.org>
Date: Thu, 13 Mar 2003 13:10:24 +0000
Message-Id: <>
To: pat hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org
Cc: Ian Horrocks <horrocks@cs.man.ac.uk>

This made me think of something (maybe) related.  Is this a reasonable 
inference rule to contemplate?:

    _:foo rdfs:label "cat"@en


    _:foo rdfs:label "chat"@fr


One could imagine similar inferences regarding comments.


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 
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Graham Klyne
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Received on Thursday, 13 March 2003 08:34:31 UTC

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