- From: Bernard Vatant <bernard.vatant@mondeca.com>
- Date: Tue, 29 Jul 2008 16:09:53 +0200
- To: Antoine Isaac <aisaac@few.vu.nl>
- Cc: "Houghton,Andrew" <houghtoa@oclc.org>, public-swd-wg@w3.org, public-esw-thes@w3.org
Hello all Since this issue is back on the table, let me put here a (hopefully clear) proposal based on both the general "natural understanding" of broader and narrower, and its formal mathematical interpretation as "strict partial orders".See http://en.wikipedia.org/wiki/Partially_ordered_set#Strict_and_non-strict_partial_orders Seems to me that there are backward compatibility, terminology, hence marketing issues here, beyond logical foundationn of the concepts. If "broader" and "narrower" do not convey the most intuitive semantics, we're bound to endless misunderstandings and have to explain again and again why it is specified in such a counter-intuitive way. People will buy more easily "closeRelative" defined as a subproperty of "relative" than "relative" being defined as a subproperty of "generalRelative", with small prints explaining that "relative" means actually "direct relative". Her is my proposal skos:broader and skos:narrower are the most generic relationships. They are irreflexive and transitive (in other words, they define strict partial orders). It's bound to applications to figure how they implement the transitivity (asserted vs computed triples). skos:maximalNarrower and skos:minimalBroader are used to define "direct" narrower and broader concepts A "minimalBroader" of X is indeed mathematically defined as being a minimal element, relative to the broader relationship, of the set of all broader concepts of X. http://en.wikipedia.org/wiki/Minimal_element In other words (X skos:minimalBroader Y) iff (X skos:broader Y) AND {Z | (X skos:broader Z) and (Z skos:broader Y)} is the empty set Similar definition for skos:maximalNarrower By definition : skos:minimalBroader rdfs:subPropertyOf skos:broader skos:maximalNarrower rdfs:subPropertyOf skos:narrower Although it conveys under different names the same idea as skos:broader rdfs:subPropertyOf skos:broaderTransitive, I think it's easier to swallow because of the names. :-) Now something very important, and orthogonal to the terminological debate: the sets of minimalBroader and maximalNarrower concepts of a given X can only be entailed from the set of broader and narrower concepts *in a closed world*. IOW in a well-defined RDF graph (e.g. inside a declared Concept Scheme). Actually the declaration of skos:minimalBroader or skos:maximalNarrower does not make much sense in an open world, where they can be easily be made inconsistent : one can always insert some concept between X and Y. The notion of empty set does not apply to an open world. So the recommandation could be that those properties should not be *declared* in vocabularies, but *computed* as necessary on the basis of available assertions at run time, that is, in the closed world of assertions available here and now. Bernard Antoine Isaac a écrit : > > Dear Andrew, > >> It also seems to me that there is a problem with this flip/flop of >> skos:broader and skos:narrower being transitive. SKOS now specifies >> skos:broader and skos:narrower to be non-transitive, but >> skos:broaderTransitive and skos:narrowerTransitive are a sub-property >> of skos:broader and skos:narrower respectively. This implies to me, >> not being an RDF/OWL expert, that skos:broaderTransitive and >> skos:narrowerTransitive inherit non-transtivity from skos:broader and >> skos:narrower respectively, and that just seems funky since you are >> saying that the relationship is transitive. >> > > The problem of transitivity "inheritance" (or more precisely > non-inheritance) problem has been many times raised, and many mails > have been written about it. > Cf http://lists.w3.org/Archives/Public/public-swd-wg/2008Jun/0102.html > > Now, I'm afraid we cannot do otherwise. Whatever being the naming > decisions in the end: > - there is need non-transitive "broader-as-asserted" property > (skos:broader) > - there is a need for a transitive "broader-as-get-me-all-ancestors" > (skos:broaderTransitive) > - there is a need to infer that every asserted direct broader > statement shall be interpreted in a way that allows to get a > transitive version of the hierarchy (I assume that you too have this > requirement) > And for the third you have no choice but to declare the first property > a subproperty of the second. That's just the way OWL is made, even if > it may appear counter-intuitive :-( > The nice thing is that in OWL doing so does not enforce skos:broader > to be transitive... > > Best, > > Antoine > > > > > No virus found in this incoming message. > Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: > 270.5.6/1577 - Release Date: 28/07/2008 06:55 > > > -- *Bernard Vatant *Knowledge Engineering ---------------------------------------------------- *Mondeca** *3, cité Nollez 75018 Paris France Web: www.mondeca.com <http://www.mondeca.com> ---------------------------------------------------- Tel: +33 (0) 971 488 459 Mail: bernard.vatant@mondeca.com <mailto:bernard.vatant@mondeca.com> Blog: Leçons de Choses <http://mondeca.wordpress.com/>
Received on Tuesday, 29 July 2008 14:10:51 UTC