A subclass of B A instance of 'type of B' B subclass of 'C' B instance of 'type of C' C subclass of 'D' C instance of 'type of D' It's a bit more subtle than that, as, let's take the Taxonomy example, and take the <animal> class. Old classifications used to take <fish> as a taxon. It is proved right now that fish is not a clade. It's still a subclass of <animal> though. I claim <fish> subclass of <animal> is still correct. <fish> is an old taxon. But <fish> instance of <clade> is not true. If someone want to search for direct subclasses of "animal", he would still have "fish" as a result, maybe. Although if he is interested in clades only my approach works, and he would get a closer approximation of what modern taxonomy tree is.

I'm still talking of the model I proposed in my first post in this thread. I did give an advantage : you can really simply query the type of units used by a country to class his administrative units, like <Region>, <Departement> (as two items) for France with just simple in one request of the future simple query module : just retrieve the instances of the class <French type of administrative units>. This model also apply to any country administrative territorial division. I think <French type of administrative units> is the "auxiliary item" markus did mention. We can define precisely what it is becaus this class <French type of administrative units> regroups the types used by france to class cities, departments ... so clearly if we talk of "Paris", there is several possibility, like the region of Paris, the City of Paris ... <The city of Paris> item is clearly the only one who is clearly defined by french law, hence it is an instance of the class <French ville>, who in turn is an instance of <French type of administrative units>. This seems to me a useful model, who can generalise easily to class things like "Urban units", who are used for statistical purpose and are defined by national statistical organism in each country, such as INSEE in france Then we could also have a <Urban unit> class in Wikidata, but this is ambiguous. This class could have a subclass <Urban unit as defined by INSEE>, with instances such as <Parisian urban unit>, for hich it gives statistical information. <Urban unit as defined by INSEE> in turn may be a subclass of <any geographical unit defined by INSEE>. Then if you want INSEE geographical units, you query all instances of both <Urban unit> and <any geographical unit defined by INSEE>. But now let's say you want to find the definition of urban unit by the INSEE itself, not the instances. One way to do that would be to look at the subclass tree of <any geographical unit defined by INSEE> or the one of <Urban unit>, or compute the intersection of both trees. One alternative, using metamodelling this time, would be to have a class regrouping all definitions of statistical units used by INSEE. Those definitions identify to some class we already have, such as <Urban unit as defined by INSEE> identifies to the definition of urban unit by INSEE. Then the class of all definitions used by INSEE would identify to the class of all classes with a name <... unit defined by INSEE>. I propose to create the item <any type of unit defined by INSEE> ; with <Urban unit as defined by INSEE> an instance of it (actually I might have already have done it /o\) This is an (non mutually exclusive, more complementary) alternative to just class administrative units instances. In a way, this is just identifying (reifying) a classification system and putting an ''instance of'' <this item> statements to its classes. I think this is interesting in Wikidata as we actually are using a lot of different classification system, having a clear and practicable pattern like this one, using just a few tools like reasonator, is useful. For example if I want to compute the subclass tree of statistical units, but only the classes used by INSEE, I can compute the subclass tree of the <statistical geographical unit> class but filtering only the instances of <any type of unit defined by INSEE>, instead of computing a tree intersection. This kind of patterns occurs also for example in biological taxonomy. They use classes such as "Genera", "taxon", "clade". Imo any instance of taxon can be seen as a class of living organisms. Then Taxon is a class of class, just as <any type of unit defined by INSEE> can be seen by a class of class. <Clade> is a subclass of taxon because any clade is a taxon. So clade is also a class of class. This makes this pattern actually already used, and studied in the world of semantic web. As it's simple and can be found in a lot of domains, I think we should use it in Wikidata. 2014-06-11 11:51 GMT+02:00 Gerard Meijssen &lt;gerard.meijssen(a)gmail.com&gt;om>: Hoi, _______________________________________________ Wikidata-l mailing list Wikidata-l(a)lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikidata-l