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RE: [MMSEM] Music Use Case & FOAF

From: Hausenblas, Michael <michael.hausenblas@joanneum.at>
Date: Thu, 29 Mar 2007 11:55:25 +0200
Message-ID: <768DACDC356ED04EA1F1130F97D298520108D25B@RZJC2EX.jr1.local>
To: RaphaŽl Troncy <Raphael.Troncy@cwi.nl>, "Yves Raimond" <yves.raimond@elec.qmul.ac.uk>
Cc: "Oscar Celma" <ocelma@iua.upf.edu>, "Michiel Hildebrand" <Michiel.Hildebrand@cwi.nl>, <public-xg-mmsem@w3.org>


Gentlemen,

I found your discussion so far very interesting, may I chime in here?

Raphael mentioned a SWBPD-WG note where the 'inverse' issue might have been mentioned.
I myself am just aware of [1] that discusses this issue w.r.t. n-ary relations, 
and a suggested note [2] from 2005, which tackles the problem in the context
of transitive props.

Another source that might be of interest is the RDF/OWL Representation of WordNet [1].
IMHO they have quite comparable objectives there, so looking at section "4. Advanced options",
tells us:

" ... the WordNet data does not explicitly contain the inverse of e.g. hyponymOf.
The inverse statement is only implied with the OWL statement hyponymOf owl:inverseOf hypernymOf. 
In other words, querying the hypernymOf relation will return no results when using software
that is not OWL-aware. Therefore, RDFS users should not use the inverse properties because they
do not yield query results. Because querying for X hypernymOf Y is just a syntactic variant of
querying for Y hyponymOf X RDFS users do not have less information than OWL users."

Does this help?

Cheers,
	Michael

[1] http://www.w3.org/TR/swbp-n-aryRelations/#choosingPattern1or2
[2] http://www.w3.org/2001/sw/BestPractices/OEP/#suggest
[3] http://www.w3.org/TR/wordnet-rdf/

----------------------------------------------------------
 Michael Hausenblas, MSc.
 Institute of Information Systems & Information Management
 JOANNEUM RESEARCH Forschungsgesellschaft mbH
  
 http://www.joanneum.at/iis/
----------------------------------------------------------
 

>-----Original Message-----
>From: public-xg-mmsem-request@w3.org 
>[mailto:public-xg-mmsem-request@w3.org] On Behalf Of RaphaŽl Troncy
>Sent: Thursday, March 29, 2007 11:10 AM
>To: Yves Raimond
>Cc: Oscar Celma; Michiel Hildebrand; public-xg-mmsem@w3.org
>Subject: Re: [MMSEM] Music Use Case & FOAF
>
>
>Dear Yves,
>
>Thanks for your answers.
>
>> In fact, I think there is a misunderstanding here. MO is a 
>RDF-schema,
>> not a full-fledged DL ontology.
>
>I understood that ... but not that now RDFS has model-theory 
>semantics, there is not
>much difference, just less entailment rules.
>
>> But the point of MO was to dump *huge* repositories in RDF
>> (musicbrainz, cc databases...), and we did not want to make the
>> "ontology" too complex, to finally have multiple rdf sources
>> expressing the same thing in a lot of different ways, and making the
>> assumption that either the RDF provider (which is not feasable for
>> this amount of data) or the "consumer" can cope with that. Well,
>> that's ok, but you make a strong assumption on its capabilities.
>
>I think I understand that, and I have the same argument, but 
>with a different
>conclusion. Because I don't want to make the ontology 
>"complex", I don't want to impose
>a single way to express things. And I don't make assumptions 
>about what the RDF provider
>or consummer should cope with, I let the SemanticWeb taking 
>care of that. The tools are
>here, the complexity is not high, there are no technological 
>challenges, we have just to
>use them :-)
>
>> Finally: anyone can add a more complete OWL
>> layer on top of it.
>
>Yes, and this is exactly what will happen, which I think is a 
>shame given the the great
>job you did.
>I have never claimed that we _should_ have inverse properties 
>for everything, just when
>it is useful, and in this case, it seems so natural ! Because 
>we are talking about
>songs, tracks, the point of interest of many applications ! In 
>your situation, I need to
>describe an album for knowing its track. But if I don't care 
>about the other tracks, it
>is a quite non natural way of describing the knowledge.
>
>I will put you the problem in the other way around. Properties 
>are directed in RDF: you
>specify a domain and a range. When you define a property (and 
>its way) you make a
>modeling decision according to the common use of this property in your
>domain/application. For example, you will either decide that: 
>ex:bag ex:contains
>ex:object OR ex:object ex:is_contained ex:bag
>If both the domain and the range classes are equally 
>used/important in your domain, then
>you should better defined both properties, marked as inverse. 
>I think the Semantic Web
>Best Practices Working Group has written a note about that.
>
>> I don't see why not defining inverses for all properties
>> in a particular ontology goes against it. It is an open-world, as you
>> say: so everyone is free to just write a small RDF document:
>> mo:has_track owl:inverseOf myDLmo:is_in_album
>> and publish it on the web.
>
>You're right, and this is what will happen. But then you 
>reduce the usability of your
>ontology, because you almost force people (at least us) to 
>define this inverse property
>where we would prefer that this property would be defined in 
>the MO namespace.
>
>> (Shameless plug: you should take a look at the Linking
>> Open Data project of SWEO [1]).
>
>Thanks, this is indeed a very interesting link.
>
>> And I don't think FOAF has a foaf:is_known_by property:-) We are here
>> in the same sort of case.
>
>Well not really. It depends on your application. What is the 
>most important: the persons
>you know, or the persons that know you?
>FOAF considers that the first one is more important. If they 
>were equally important,
>then it certainly worth to have both properties.
>In your case, I strongly believe that BOTH the albums and the 
>tracks are first class
>objects, equally important, and that you should be able to 
>provide statements on them
>without the other.
>
>> In most large-scale available rdf repositories, there is no 
>reasoning.
>
>Well, here I disagree. About which (large-scale) RDF 
>repositories you're talking ?
>Sesame 1, 2, JENA, SWI-Prolog, OWLIM, KAON, RDFSuite, rdfDB, 
>Redland, etc ... all have
>RDF+RDFS reasoning support ...
>
>> (Btw, what do you mean by "forward chaining at querying time"?
>
>I just mean the reasoning is performed during the query and 
>not by saturating your
>knowledge base when you upload new data as it is usually the 
>case for optimization.
>SPARQL does not do forward chaining.
>
>>  * It has the inverse of most of its properties, but marked as
>> unstable, as well as anything OWL inside it (look at the section
>> "DL-candies" in the RDFS file:-) )
>
>Hummm, I miss that. Is there a named property in MO, inverse 
>of "mo:has_track"?
>This is all I want :-)
>
>Best regards.
>
>    RaphaŽl
>
>--
>RaphaŽl Troncy
>CWI (Centre for Mathematics and Computer Science),
>Kruislaan 413, 1098 SJ Amsterdam, The Netherlands
>e-mail: raphael.troncy@cwi.nl & raphael.troncy@gmail.com
>Tel: +31 (0)20 - 592 4093
>Fax: +31 (0)20 - 592 4312
>Web: http://www.cwi.nl/~troncy/
>
>
>
>
Received on Thursday, 29 March 2007 09:52:05 GMT

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