As someone relatively new to Wikidata, I need to ask for some help understanding the following paragraph from the forwarded email:
Please note that *instance of* (P31) and *subclass of* (P279) are not valid values for *subproperty of* (P1647) claims, as described in the P1647 documentation [1]. For example, claims like "occupation *subproperty of* instance of" are invalid. What specifically in the P1647 documentation [1] describes that *instance of* (P31) and *subclass of* (P279) are not valid values for *subproperty of* (P1647) claims? [1]https://www.wikidata.org/wiki/Property:P1647 Thanks, James Weaver On Sat, Jan 10, 2015, at 02:25 PM, Emw wrote: > Since it appears that the creation of *subproperty of* went unnoticed > by many, I'd like to describe an important aspect of its proper use, > and how that relates to classification. > > Please note that *instance of* (P31) and *subclass of* (P279) are not > valid values for *subproperty of* (P1647) claims, as described in the > P1647 documentation [1]. For example, claims like "occupation > *subproperty of* instance of" are invalid. The reasons for this are > both technical and architectural. > > On the technical side, *instance of, subclass of* and *subproperty of* > are intended to be straightforwardly exportable as rdf:type, > rdfs:subClassOf and rdfs:subPropertyOf. As described in *On the > Properties of Metamodeling in OWL* [2], claims that use OWL's built-in > vocabulary (e.g. rdf:type) as individuals make an ontology > undecidable. If an ontology is undecidable, then queries are not > guaranteed to terminate. This is a big deal. Decidability is a main > goal of OWL 2 DL and a requirement in the more specialized profiles > OWL 2 EL, OWL 2 RL and OWL 2 QL. Most Semantic Web ontologies aim to > valid be in at least OWL 2 DL. So if Wikidata aims to be easily > interoperable with the rest of the Semantic Web, we should aim to be > valid in OWL 2 DL, and thus not make claims of the form "P > *subproperty of* instance of (P31)" or "P *subproperty of* subclass of > (P279)". > > Avoiding such claims is also good design. There should be one -- and > preferably only one -- obvious way to specify the type of an instance. > Having a multitude of domain-specific "type" subproperties would > promote an anti-pattern: using *instance of* as a catch-all property > to make any statement under the sun that makes sense when connected > with the phrase "is a". > > Having a single "type" property for instances also fosters another > best practice in Wikidata: asserted monohierarchy [3]. In other words, > there should be only one explicit normal or preferred *instance of *or > *subclass of* claim per item. Having an *instance of *claim and a > *subclass of* claim on an item isn't necessarily bad (it's called > "punning"), but having multiple *instance of* claims or multiple > *subclass of* claims on an item is a bad smell. Items can typically > satisfy a huge number of *instance of* claims, but should generally > have only one such claim made explicitly in Wikidata. > > For example, Coco Chanel (Q45661) can be said to be "*instance of* > French person", "*instance of* fashion designer", "*instance of* > female", etc. Instead of such catch-all use of *instance of*, Wikidata > moves that knowledge into properties like *country of citizenship* > (P27), *occupation* (P106) and *sex or gender* (P21). Coco Chanel has > one explicit *instance of* value: human (Q5) -- a class that > encapsulates essential features of the subject. > > Most of Wikidata follows these general principles of classification. > But a few domains of knowledge remain either somewhat of a mess, or > organized but idiosyncratic. Items like the one for the German > municipality of Aalen [4], with 7 *instance of* values -- several of > them redundant -- exemplify the mess. With the deletion of > domain-specific "type" properties like *type of administrative > territorial entity* (P132) [5], we are on the right track. The > solution is not to make such things subproperties of *instance of*, > but rather to delete them and use *instance of* for one preferred > class and put other values in other properties (note -- this may > require new properties!). > > The same applies for *subclass of*. > > I encourage anyone interested in stuff like *subproperty of* to join > the discussions ongoing at > https://www.wikidata.org/wiki/Wikidata:Property_proposal/Property_metadata. > The Wikidata community is currently discussing how we want to handle > things like *domain* and *range* properties (e.g. should we use > rdfs:domain or schema:DomainIncludes?) and whether we want to have an > *inverse of* property (or delete all inverse properties). The outcome > of these discussions will shape the interface between Wikidata and the > rest of the Semantic Web. > > Thanks, Eric > > https://www.wikidata.org/wiki/User:Emw > > > 1.https://www.wikidata.org/wiki/Property:P1647 > 2.Boris Motik (2007). On the Properties of Metamodeling in > > OWL.**https://www.cs.ox.ac.uk/boris.motik/pubs/motik07metamodeling-journal.pdf** > *3. *Barry Smith, Werner Ceusters (2011). Ontological realism: A > methodology for coordinated evolution of scientific ontologies. > Section 1.8: Asserted monohierarchies. > http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104413/#S9** > 4.Aalen on Wikidata as of 2015-01-10. > https://www.wikidata.org/w/index.php?title=Q3951&oldid=184247296#P31 > 5.https://www.wikidata.org/wiki/Wikidata:Requests_for_deletions/Archive/2014/Properties/1#type_of_administrative_territorial_entity_.28P132.29 > _________________________________________________ > Wikidata-l mailing list Wikidata-l@lists.wikimedia.org > https://lists.wikimedia.org/mailman/listinfo/wikidata-l
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