- From: Graham Klyne <GK@NineByNine.org>
- Date: Thu, 13 Mar 2003 13:10:24 +0000
- 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 implies _:foo rdfs:label "chat"@fr ? 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 >-- >--------------------------------------------------------------------- >IHMC (850)434 8903 or (650)494 3973 home >40 South Alcaniz St. (850)202 4416 office >Pensacola (850)202 4440 fax >FL 32501 (850)291 0667 cell >phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes >s.pam@ai.uwf.edu for spam ------------------- Graham Klyne <GK@NineByNine.org> PGP: 0FAA 69FF C083 000B A2E9 A131 01B9 1C7A DBCA CB5E
Received on Thursday, 13 March 2003 08:34:31 UTC