Hi Thomas,
On 15/05/14 11:47, Thomas Douillard wrote:
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 ?
I agree with what you say. It is impossible to build a redundancy-free
Wikidata (think of property "spouse" ;-), and there are several reasons
for allowing for some kinds of redundancy. At the same time, we could
never store *every* fact that implicitly follows from other statements.
The community is having discussions about what should be in and what
should be out, based on concrete use-cases (for example, we don't have
"grandparent" but we do have "sister"). In the end, we have to leave
this to the experts in each topic area.
I applaud your comparison of inferencing with a form of decompression. I
think this is a nice intuition (in fact, some people have researched
"semantic compression" where one tries to reduce the size of a knowledge
base by eliminating things that follow from the rest anyway).
You are right that the ramifications of removing one statement might be
bigger if inferences are used. On the other hand, there are many other
reasons why a single change can have a big impact: soon we will have
simple queries, and it is quite possible that thousands of template
instances issue queries that all depend on the same single statement --
deleting it would change a lot of pages then. Redundancy cannot protect
against this, since most queries (or inference rules) would refer to one
form of the data and not check all possible redundant formulations.
Moreover, many things in Wikidata are not stored redundantly at all, yet
we want robustness in all cases. A mechanism to indicate importance like
you describe might be a solution, or we could use a form of protection
to avoid accidental changes to important statements. But this is yet
another discussion, which is probably more important for Wikipedia than
for the prototype I was having in mind.
Another interesting use of inferencing in a system that has redundancy
could be to infer additional support for a statement (Example: if a
reference says that X is a child of Y, then the same reference also
supports the claim that Y is the parent of X). In other words: even if
we don't want to infer statements, we might want to infer references :-)
Constraints are a great start. We should now ask how we could improve
the management of constraints in the future, and which constraints we
will have then.
Cheers,
Markus
2014-05-14 15:33 GMT+02:00 Markus Krötzsch
<mar...@semantic-mediawiki.org <mailto:mar...@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&lang=en
<http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q35120&rp=279&lang=en>
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
<https://www.wikidata.org/wiki/User:Emw>
[1]
https://www.wikidata.org/wiki/__WT:MB#Distinguishing_between___genes_and_proteins
<https://www.wikidata.org/wiki/WT:MB#Distinguishing_between_genes_and_proteins>
[2] https://www.wikidata.org/wiki/__WT:MB#Human.2Fmouse.2F..._ID
<https://www.wikidata.org/wiki/WT:MB#Human.2Fmouse.2F..._ID>
[3] https://www.wikidata.org/wiki/__User:ProteinBoxBot
<https://www.wikidata.org/wiki/User:ProteinBoxBot>. Chinmay Nalk
(https://www.wikidata.org/__wiki/User:Chinmay26
<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
<https://www.wikidata.org/wiki/Wikidata:WikiProject_Mineralogy>
[5]
http://tools.wmflabs.org/__wikidata-todo/tree.html?q=__Q15281399&rp=279&lang=en
<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&lang=en
<http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q796194&rp=279&lang=en>
[7] http://apps.who.int/__classifications/icd10/browse/__2010/en
<http://apps.who.int/classifications/icd10/browse/2010/en>
[8] https://en.wikipedia.org/wiki/__Template:Surgeries
<https://en.wikipedia.org/wiki/Template:Surgeries>
[9]
https://www.wikidata.org/w/__index.php?title=Wikidata:__Database_reports/Popular___properties&oldid=125595374
<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#__chemical_element
<https://www.wikidata.org/wiki/Wikidata:Project_chat#chemical_element>
-
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/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
<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&lang=en
<http://tools.wmflabs.org/wikidata-todo/tree.html?q=Q164950&rp=279&lang=en>
[12] http://korrekt.org/page/The___Incredible_ELK
<http://korrekt.org/page/The_Incredible_ELK>
[13] https://www.mediawiki.org/__wiki/Wikidata_Toolkit
<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.kroetz...@tu-dresden.de>
<mailto:markus.kroetzsch@tu-__dresden.de
<mailto:markus.kroetz...@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
of thousands.
(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
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