Hi Markus.
Concerning redundancy, I question myself. Is redundancy, at least at some degree, something we absolutely want to remove from Wikidata ? I don't think so. Wikidata is an open project where a lot of change happens on a high number of "pages" (in the Wiki sense). This mean in my own the more control mechanism there is the best it is.
I think redundancy is a powerful mechanism in robustness achievment, it happens to some extent in a lot of complex systems. For example think of claim deletion. Assume a reasoner would rely on that claim to make a lot of inferences. In a sense it's a kind of compression of information. Then there is a risk, if the deletion is unnoticed, that we lose a lot of datas due to that claim deletion.
Now think that there is a redundant claim that is a part of the inferences chain that come from our deleted claim, could a mechanism based on inferences enlight the fact that the graph might be incomplete, or that the deletion introduced an inconsistency, or whatever, where just a inference system with a minimal set of claim to compress the stored data would just not make the inference anymore ? I guess it could also compare the (would we say completed graph, or partially completed ?) before and after the change, and hint that there actually is a mass loss of datas. Or compute a "inference score" based on the number of inferences a claim is a part of to hint the patrollers for the deletion to verify (just random thoughts.
Anyway, any thoughts on redundancy in Wikidata ?
2014-05-14 15:33 GMT+02:00 Markus Krötzsch markus@semantic-mediawiki.org:
Hi Eric,
Thanks for all the information. This was very helpful. I only get to answer now since we have been quite busy building RDF exports for Wikidata (and writing a paper about it). I will soon announce this here (we still need to fix a few details).
You were asking about using these properties like rdfs:subClassOf and rdf:type. I think that's entirely possible, since the modelling is very reasonable and would probably yield good results. Our reasoner ELK could easily handle the class hierarchy in terms of size, but you don't really need such a highly optimized tool for this as long as you only have subClassOf. In fact, the page you linked to shows that it is perfectly possible to compute the class hierarchy with Wikidata Query and to display all of it on one page. ELK's main task is to compute class hierarchies for more complicated ontologies, which we do not have yet. OTOH, query answering and data access are different tasks that ELK is not really intended for (although it could do some of this as well).
Regarding future perspectives: one thing that we have also done is to extract OWL axioms from property constraint templates on Wikidata talk pages (we will publish the result soon, when announcing the rest). This gives you only some specific types of OWL axioms, but it is making things a bit more interesting already. In particular, there are some constraints that tell you that an item should have a certain class, so this is something you could reason with. However, the current property constraint system does not work too well for stating axioms that are not related to a particular property (such as: "Every [instance of] person who appears as an actor in some film should be [instance of] in the class 'actor'" -- which property or item page should this be stated on?). But the constraints show that it makes sense to express such information somehow.
In the end, however, the real use of OWL (and similar ontology languages) is to remove the need for making everything explicit. That is, instead of "constraints" (which say: "if your data looks like X, then your data should also include Y") you have "axioms" (which say: "if your data looks like X, then Y follows automatically"). So this allows you to remove redundancy rather than to detect omissions. This would make more sense with "derived" notions that one does not want to store in the database, but which make sense for queries (like "grandmother").
One would need a bit more infrastructure for this; in particular, one would need to define "grandmother" (with labels in many languages) even if one does not want to use it as a property but only in queries. Maybe one could have a separate Wikibase installation for defining such derived notions without needing to change Wikidata? There are no statements on properties yet, but one could also use item pages to define derived properties when using another site ...
Best regards,
Markus
P.S. Thanks for all the work on the "semantic" modelling aspects of Wikidata. I have seen that you have done a lot in the discussions to clarify things there.
On 06/05/14 04:53, emw wrote:
Hi Markus,
You asked "who is creating all these [subclass of] statements and how is this done?"
The class hierarchy in http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q35120&rp=279&lan... shows a few relatively large subclass trees for specialist domains, including molecular biology and mineralogy. The several thousand subclass of 'gene' and 'protein' subclass claims were created by members of WikiProject Molecular biology (WD:MB), based on discussions in [1] and [2]. The decision to use P279 instead of P31 there was based on the fact that the "is-a" relation in Gene Ontology maps to rdfs:subClassOf, which P279 is based on. The claims were added by a bot [3], with input from WD:MB members. The data ultimately comes from external biological databases.
A glance at the mineralogy class hierarchy indicates it has been constructed by WikiProject Mineralogy [4] members through non-bot edits. I imagine most of the other subclass of claims are done manually or semi-automatically outside specific Wikiproject efforts. In other words, I think most of the other P279 claims are added by Wikidata users going into the UI and building usually-reasonable concept hierarchies on domains they're interested in. I've worked on constructing class hierarchies for health problems (e.g. diseases and injuries) [5] and medical procedures [6] based on classifications like ICD-10 and assertions and templates on Wikipedia (e.g. [8]).
It's not incredibly surprising to me that Wikidata has about 36,000 subclass of (P279) claims [9]. The property has been around for over a year and is a regular topic of discussion [10] along with instance of (P31), which has over 6,600,000 claims.
You noted a dubious claim subclass of claim for 'House of Staufen' (Q130875). I agree that instance of would probably be the better membership property to use there. Such questionable usage of P279 is probably uncommon, but definitely not singular. The dynasty class hierarchy shows 13 dubious cases at the moment [11]. I would guess less than 5% of subclass of claims have that kind of issue, where instance of would make more sense. I think there are probably vastly more cases of the converse: instance of being used where subclass of would make more sense.
As you probably know, P31 and P279 are intended to have the semantics of rdf:type and rdfs:subClassOf per community decision. A while ago I read a bit about the ELK reasoner you were involved with [12], which makes use of the seemingly class-centric OWL EL profile. Do you have any plans to integrate features of ELK with the Wikidata Toolkit [13]? How do you see reasoning engines using P31 and P279 in the future, if at all?
Thanks, Eric
https://www.wikidata.org/wiki/User:Emw
[1] https://www.wikidata.org/wiki/WT:MB#Distinguishing_between_ genes_and_proteins [2] https://www.wikidata.org/wiki/WT:MB#Human.2Fmouse.2F..._ID [3] https://www.wikidata.org/wiki/User:ProteinBoxBot. Chinmay Nalk (https://www.wikidata.org/wiki/User:Chinmay26) did all the work on this, with input from WD:MB. [4] https://www.wikidata.org/wiki/Wikidata:WikiProject_Mineralogy [5] http://tools.wmflabs.org/wikidata-todo/tree.html?q= Q15281399&rp=279&lang=en [6] http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q796194&rp=279&la... [7] http://apps.who.int/classifications/icd10/browse/2010/en [8] https://en.wikipedia.org/wiki/Template:Surgeries [9] https://www.wikidata.org/w/index.php?title=Wikidata: Database_reports/Popular_properties&oldid=125595374 [10] Examples include
https://www.wikidata.org/wiki/Wikidata:Project_chat/Archive/ 2013/12#Top_of_the_subclass_tree
https://www.wikidata.org/wiki/Wikidata:Project_chat/Archive/ 2014/01#Question_about_classes.2C_and_.27instance_of.27_vs_.27subclass.27 [11] http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q164950&rp=279&la... [12] http://korrekt.org/page/The_Incredible_ELK [13] https://www.mediawiki.org/wiki/Wikidata_Toolkit
On Mon, May 5, 2014 at 12:46 PM, Markus Kroetzsch <markus.kroetzsch@tu-dresden.de mailto:markus.kroetzsch@tu-dresden.de>
wrote:
Hi, I got interested in subclass of (P279) and instance of (P31) statements recently. I was surprised by two things: (1) There are quite a lot of subclass of statements: tenth ofthousands. (2) Many of them make a lot of sense, and (in particular) are not (obvious) copies of Wikipedia categories.
My big question is: who is creating all these statements and how is this done? It seems too much data to be created manually, but I don't see obvious automated approaches either (and there are usually no references given). I also found some rare issues. "A subclass of B" should be read as "Every A is also a B". For example, we have "Every piano (Q5994) is also a keyboard instrument (Q52954)". Overall, the great majority of cases I looked at had remarkably sane modelling (which reinforces my big question). But there are still cases where "subclass of" is mixed up with "instance of". For example, Wikidata also says "Every 'House of Staufen' (Q130875) is also a dynasty (Q164950)". This is dubious -- how many instances of 'House of Staufen' are there? I guess we really want to say that "The House of Staufen is a(n instance of) dynasty." Is this a singular error or a systematic issue? I guess there is already a group of people who deal with such issues -- or it would be a miracle that things are in such a good shape already :-) I have read the talk page for subclass of, but that does not seem to explain the original of all the data we have already. Pointers? Cheers, Markus _________________________________________________ Wikidata-l mailing list Wikidata-l@lists.wikimedia.org <mailto:Wikidata-l@lists.wikimedia.orghttps://lists.wikimedia.org/__mailman/listinfo/wikidata-l <https://lists.wikimedia.org/mailman/listinfo/wikidata-l>
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