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Re: [swikig] [Semediawiki-user] Semantics of MW Categories and OWL

Chronological Thread 
  • From: "Uschold, Michael F" <michael.f.uschold AT>
  • To: "Yaron Koren" <yaron57 AT>
  • Cc: "Clark, Peter E" <clarkp AT>, "Jones, David H" <david.h.jones AT>, semediawiki-user AT, "Kitzmiller, Ted" <ted.kitzmiller AT>, mediawiki-l AT, "Folger, Deborah H" <deborah.h.folger AT>, "Murray, William R" <William.R.Murray AT>, swikig AT
  • Subject: Re: [swikig] [Semediawiki-user] Semantics of MW Categories and OWL
  • Date: Mon, 6 Aug 2007 10:54:03 -0700
  • Envelope-to: swikig AT
  • List-archive: <>
  • List-id: Semantic Wiki Interest Group <>

Yaron said:
"though categories are used for many things in MediaWiki, in Semantic MediaWiki they should really only be used to indicate instances and subclasses"
I'm now getting this.  However, the documentation about Annotation in SMW says:
"Categories can have many different interpretations. For example, the category "City" might comprise of all articles about cities, i.e. it describes that something is a city. Other categories, such as the category "Mathematics," might rather describe the topic area of an article. Many other interpretations exist. Semantic MediaWiki endorses this practical usage of categories: categories should be used to describe collections of articles that are considered useful or interesting for users."
How can this be? It seems to directly conflict what many have said, that Categories in SMW should only be used as follows:
* a category of a category is a subclass
* an article of a category is an instance
If you use them differently, then bad things will happen when the translation to RDF happens, and when hierarchical inference occurs, as per my original message on this theme when you use Category for a mix of partOf, instanceOf, subClassOf, isAboutTopic, etc.
I'm inclined to think this is mistaken, or at best, confusing/misleading.

Michael Uschold
M&CT, Phantom Works
425 373-2845
michael.f.uschold AT 

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From: Yaron Koren [mailto:yaron57 AT]
Sent: Saturday, August 04, 2007 6:40 AM
To: Uschold, Michael F
Cc: Danny Ayers; Jones, David H; Folger, Deborah H; mediawiki-l AT; Murray, William R; semediawiki-user AT; Clark, Peter E; Kitzmiller, Ted; swikig AT
Subject: Re: [Semediawiki-user] [swikig] Semantics of MW Categories and OWL

Hi Michael,

In answer to your specific questions about categories, you should check out this thread from a month ago: AT . Long story short, though categories are used for many things in MediaWiki, in Semantic MediaWiki they should really only be used to indicate instances and subclasses (and the way to differentiate between those two is that one is itself a category and the other is not).

Also, you can avoid having a template itself be part of a category through use of the "<includeonly>" tag.


On 8/4/07, Danny Ayers <danny.ayers AT> wrote:
On 04/08/07, Uschold, Michael F <michael.f.uschold AT> wrote:
> The semantics of categories in Media Wiki seems to be too general, so that
> it is not amenable to linking up with OWL.

With OWL DL, I believe you're right. But this doesn't rule out using
parts of OWL (e.g. <categoryA> owl:sameAs <categoryB>) under OWL Full.

It may be possible to apply the usual trick of indirection to get
around the problem you describe. I've not looked closely, but
categories could perhaps be wrapped into SKOS [1] concepts, so the
reasoning would be over properties like broader/narrower, without the
potential inconsistencies brought on through using subclass
relationships directly. (Not unrelated is the Tag Ontology [2] which
uses SKOS to cover folksonomy tagging).

I don't believe it's going to solve the kind of problem you describe
overnight (especially since there appear to be other aspects that are
further from RDF/RDFS) but there may be hope on the horizon with OWL
In OWL 1.1 a name (such as Person) can be used as any or all of an
individual, a class, or a property. The computational problems that
would arise if this were treated as in RDF are avoided by ensuring
that no aspect of the use of the name as an individual has any effect
on the meaning of the name as a class. Such a treatment of
metamodeling is often called punning.




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