Re: SKOS transitive hierarchical relations

Hi Simon, Vincenzo,


>     Dear Simon, all,
>     I'm surely not an expert of SKOS, nor a librarian, but at the latest UDC
>     seminar I participated I tried to bring the point of view of my research
>     group (working in knowledge representation and reasoning) in which we
>     tried to formalize the meaning of the BT\NT relations.
>
>     We interpret them as superset/subset and let them correspond to
>     subsumption in description logic were the interpretation of each node in
>     the vocabulary is the set of documents about the node. Now, since both
>     subset and subsumption are transitive, this works only for transitive
>     BT\NT relations. We treat non transitive BTs as associative relations.
>
>
> This is mostly correct; associative relationships should be used where the relationship is not necessarily transitive for the applicable domain of discourse (which is either the subject area for which the thesaurus is defined (ISO 2788), or the entire bibliographic universe (NISO Z39.19:2005).
>
> Note that the key distinction between Knowledge Organization Systems and Knowledge Representation systems is that the latter have extensions that arbitrary things, whereas KOS's are extensional over Conceptual Works... Word and Subject v. Word and Object. Or to put it another way... http://www.ibiblio.org/ses/anyqs.jpg
>
> BTW, to clarify the Turbine and Blade example;
>
> Under the ISO rule, for a thesaurus specific to the domain of documents about turbines, if all documents about blades are necessarily documents about things which are parts of turbines, the vocabulary engineer may use the BT relationship, since there cannot exist documents about blades which are not about turbines. This relationship is prohibited under NISO Z39.19:2005.
>
> Transitivity of NT does not entail any relationship between co-hyperonyms of a given subject.
> e.g.
> (Turbine Blade NTP Turbine) AND (Turbine Blade NTG Blade) |= (Blade NT Turbine)
>
> (Parrots as Pets NT Parrots) AND (Parrots as Pets NT Pets) |= (Parrots NT Pets) OR (Pets NT Parrots).
>
> That most parrots in Western Europe and the US are pets is not expressible in a monotonic, non-probabilistic ontology language. More expressive languages can express this. PR-OWL (Kathy Lasky, Paulo Costas, and their students) can conditionalize the probabilities (P(Parrot is Pet | Location is Fairfax, VA) = 0.95); a system like Cyc can add the axiom as a default within a microtheory specialized to urban areas (Parrots that are not abnormal are Pets). Abduction can also allow one to hypothesize that a Parrot is a Pet, but that situation is better handled through a probabilistic reasoner.
>
> Part of the problem with the way that SKOS handles broader^* is that the current rationale is based on epistemic/doxastic/illocutionary concerns that could arise when using a reasoner that cannot could not distinguish between inferred and asserted object property values. Since this information is part of the OWL API (cf OWlIndividual.getObjectPropertyValues <http://owlapi.sourceforge.net/javadoc/org/semanticweb/owlapi/model/OWLIndividual.html#getObjectPropertyValues(org.semanticweb.owlapi.model.OWLObjectPropertyExpression, org.semanticweb.owlapi.model.OWLOntology)> with OwlReasoner.getObjectPropertyValues <http://owlapi.sourceforge.net/javadoc/org/semanticweb/owlapi/reasoner/OWLReasoner.html#getObjectPropertyValues(org.semanticweb.owlapi.model.OWLNamedIndividual, org.semanticweb.owlapi.model.OWLObjectPropertyExpression)> )this does not seem to be a problem with the reasoners in current use.
>
> If the underlying problem is how to handle vocabularies that use BT incorrectly, better approaches are to either fix the vocabulary (if the vocabulary is supposed to be using BT in a standard form), or, if that is not possible, to translate the relations accidentally labeled as BT as being associative. This is the treatment for quasi and pseudo broader relationships prescribed in the standards.


And this is where the design rationale of SKOS differs from the ones of standards like ISO2788. SKOS does not really specify rules on how to create vocabularies. It is just meant to port existing vocabularies as is, and not to block their publication until they are fixed by you (both Simon and Vincenzo's team). Had we enforced such rules, we'd be forced to tell id.loc.gov and many others that their data is not correct SKOS. Which we did not want to do.


>
> If you want to capture the semantics of Broader Term using the SKOS vocabulary, you should assert broaderTransitive and ignore the suggestions in the primer.


I really don't understand this. If I assert a broader statement between A and B, then SKOS says that there is a broaderTransitive between A and B, which you can exploit. So from your perspective, there should be no difference...

Antoine

>
> Simon
> p.s.
> There are possible psychological reasons to doubt the cognitive validity of the broader term relationship, but these reasons are explicitly blocked in the Standard's definitions of controlled vocabularies (most questions arise out of polysemy and from prototype effects in psychological concepts).

Received on Thursday, 5 January 2012 17:07:11 UTC