Hi! > The community-defined meaning of /subclass of/ (P279) is that of > rdfs:subClassOf [1]. Similarly, the community-defined meaning of > /instance of/ (P31) is that of rdf:type [2, 3].
Are you sure it is always correct? AFAIK there are some specific rules and meanings in OWL that classes should adhere to, also same thing can not be an individual and a class, and others (not completely sure of the whole list, as I don't have enough background in RDF/OWL). But I'm not sure existing data actually follows that. > There are some open problems with how to handle qualifiers on /instance > of/ and /subclass of/ in RDF/OWL exports of P31 as rdf:type and P279 as > rdfs:subClassOf, but that does not negate the community's decision to > tie its two most basic membership properties to those W3C standard > properties. In the current RDF/OWL exports that follow the community I'm not sure I understand how that works in practice. I.e., if we say that P31 *is* rdf:type, then it can't be qualified in RDF/OWL and we can not represent part (albeit small, qualified properties are about 0.2% of all such properties) of our data. I mean, we can certainly have data sets which include P31 statements from the data translated to rdf:type unless they have qualifiers, and that can be very useful pragmatically, no question about it. But can we really say P31 is the same as rdf:type and use it whenever we choose to represent Wikidata data as RDF? I'm not sure about that. > For example, pizza (https://www.wikidata.org/wiki/Q177) is currently > modeled as an instance of food and (transitively) a subclass of food. Here we have another practical issue - if we adhere to the strict notion that pizza is only a subclass, then we would practically never have any instances in the database for wide categories of things. I.e. since a particular food item is rarely notable enough to be featured in Wikidata, no food would have instances. It may be formally correct but I'm afraid it's not like most people think - for most people, pizza is a food, not a "subclass of food". Same with chemistry - as virtually no actual physical chemical compound (as in "this brown liquid in my test tube I prepared this morning by mixing contents of those three other test tubes") of would be notable enough to gain entry in Wikidata, nothing in chemistry would ever be an instance. Theoretically it may be sound, but practically I'm not sure it would work well, even more - that it is *already* what the consensus on Wikidata is. -- Stas Malyshev [email protected] _______________________________________________ Wikidata mailing list [email protected] https://lists.wikimedia.org/mailman/listinfo/wikidata
