From: Ian Horrocks ([email protected])
Date: 04/25/01
I have appended an email with some useful pointers relating to the earlier discussion. Ian On April 25, Lynn Andrea Stein writes: > This was the subject of some discussion within the pre-DAML RDF community as > well. I believe that what was settled on, for RDF, at least, was what you call > "restriction from above" for both domain and range. I thought some statement to > this effect was going to be made. On the other hand, RDF/S as originally written > clearly says restriction from below on domain. > > Perhaps Ralph remembers this round? > > Lynn > > > pat hayes wrote: > > > Checking thru the walk-thru. The section which introduces properties > > is worded in a way that suggests a different semantics from the one > > given in the model theory. > > > > The example says that the domain of hasParent is #Animal, and this > > clearly suggests that the intention is that this should mean that > > every animal has a parent, ie that hasParent applies to the entire > > domain class (in contrast to the range specification.) I wrote the > > following 'explanation' before realising that it might not be true: > > > > "The range specification restricts the property from 'above', ie it > > specifies a class into which the value of the property must fit, > > while the domain restricts it from 'below', ie it specifies a class > > which must be included in the class of things that the property can > > be applied to. " > > > > Is this correct?? Because if so, the semantics is wrong at this point. It says > > > > <rdfs:domain,?P,?C> means: if <x,y> in IR(?P) then x in IC(?C) > > > > but if the above is correct then it ought to say: > > > > <rdfs:domain,?P,?C> means: if x in IC(?C) then for some y, <x,y> in IR(?P) > > > > If the semantics is correct, however, then the example in the > > walkthrough is rather misleading, and we will need to correct against > > any potential misunderstanding. Also, in this case, HOW does someone > > give a 'lower' bound to the domain of a property? Eg how can one say > > that hasParent applies to *any* animal? (If both domain and range > > restrict from above, then it would be consistent to give all > > properties empty domains and ranges.) > > > > I await clarification from the Semantic Gurus, and will write > > appropriate prose for the walkthru when clarity is restored to my > > mind. > > > > Pat Hayes > > > > PS. A related question. If > > <rdfs:domain,?P,?D> > > <rdfs:range,?P,?R> > > <inverseOf,?P,?S> > > does it follow that > > <rdfs:domain, ?S,?R> > > <rdfs:range,?S,?D> > > ?? > > > > PPS. The only way to really learn something is to try teaching it to > > other people :-) > > > > --------------------------------------------------------------------- > > IHMC (850)434 8903 home > > 40 South Alcaniz St. (850)202 4416 office > > Pensacola, FL 32501 (850)202 4440 fax > > [email protected] > > http://www.coginst.uwf.edu/~phayes > ------- start of forwarded message ------- From: Jeen Broekstra <[email protected]> To: [email protected] Date: Mon, 25 Sep 2000 13:19:55 +0200 (CEST) Subject: Discussion on rdfs:range semantics on W3C RDF list Envelope-to: [email protected] Delivery-date: Mon, 25 Sep 2000 12:20:24 +0100 Hello all, as promised earlier, some pointers to the discussion that has taken place (it seems to have died out a bit now) on the RDF interest mailinglist about the semantics of rdfs:domain and rdfs:range. As some of you may know, this was especially of interest to us, since we have argued before[1] that the definition as it is now is flawed, most particularly the restriction that only one range statement is allowed. http://lists.w3.org/Archives/Public/www-rdf-interest/ is the archive of the www-rdf-interest mailinglist. http://lists.w3.org/Archives/Public/www-rdf-interest/2000Sep/0107.html is the message by Tim Berners-Lee which states that the current semantics of rdfs:range are flawed. The message contains pointers to a paper by Wolfram Conen and Reinhold Klapsing about the logical interpretation of RDFS. The ensuing discussion between TBL and Dan Brickley is interesting. http://lists.w3.org/Archives/Public/www-rdf-interest/2000Sep/0132.html is the message by me, Michel and Ian that explains the OIL-view on the semantics of domain and range. Most of the following discussion can be found in this thread. Especially the contributions of Guha, Dan Brickley and Nataly Fridman Noy are of interest. Quick summary: TBL's claim (with which Michel, Ian and I agree) is that the current semantics of domain and range are flawed. The model should allow for multiple range restrictions, and multiple restrictions should be interpreted using intersection semantics. At first I thought Guha disagreed with this view, but it seems that I misinterpreted his posting. What he says is: "Allowing multiple rdfs:domain/rdfs:range with disjunctive semantics is a bad idea because it makes the system non-monotonic. Conjunctive semantics are fine and possibly useful." I first interpreted this as a rebuttal of our approach where he accidentally mixed up conjunctive (intersection) and disjunctive (union) semantics. Now I realize that his point is probably meant in support of our claim. Anyway, the discussion is interesting for us OIL-people to read and where possible contribute. The issue is important in the sense that in a very short time a revised CR of the RDF Schema spec will be published, and all requests for change should be in by then. Regards, Jeen [1] See http://www.ontoknowledge.org/oil/papers/extending-rdfs.html -- Vrije Universiteit, Faculty of Sciences Jeen Broekstra Division of Mathematics & Computer Science [email protected] de Boelelaan 1081a http://www.cs.vu.nl/~jbroeks 1081 HV Amsterdam, the Netherlands ------- end of forwarded message -------
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