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Re: Restrictions on Bags and Seqs content

From: Michael Schneider <m_schnei@gmx.de>
Date: Wed, 11 Apr 2007 22:44:21 +0200
Message-ID: <461D48A5.9020308@gmx.de>
To: matthew.pocock@ncl.ac.uk
CC: rogargon@gmail.com, alanruttenberg@gmail.com, semantic-web@w3.org, public-owl-dev@w3.org

Hi, Matthew!

What you describe here, your array and your linked-list construction, is 
what I referred to as "custom OWLList classes", and (as far as I 
understood him) is pretty similar to what Alan Ruttenberg was about in 
his two answers to Roberto's questions. And as I said before, I think 
that such an approach (your approach!) is (technically) the best one can 
do in OWL/DL.

With my own analysis I only tried to answer Roberto's original question: 
If it is somehow possible (in OWL/DL) to use an rdf:Bag and build an 
allValuesFrom restriction for its members, and if it is good practice to 
do so. My answer was, that it /is/ possible, but with several ugly 
limitations, which few people would probably be willing to accept. So no 
good practice at all!

My opinion: One can, of course, always use a custom approach of the form 
you and Alan proposed - it works. But I suppose that many people will 
dislike the situation to always build their own custom list types, while 
there is already a lot of collection vocabulary in RDF, which they can 
only use either in a very limited way, like for rdf:Bag and friends, or 
not at all, like for rdf:List. Perhaps, it would have been wiser to not 
use 'rdf:List' in the OWL-to-RDF mappings (like e.g. for the argument 
list of owl:intersectionOf expressions), but instead use a custom 
OWLList for this purpose. This would have resulted in some 
inconveniences when writing down things like intersection expressions 
with many classes in RDF/N3 or RDF/XML, where rdf:ListS are supported by 
special syntax. But then, it would have been at least possible to use 
rdf:List in OWL axioms, if I correctly understand the situation (FIXME 
if I'm wrong!). But other people here will probably disagree with this 
view. :)


Cheers,
Michael

Matthew Pocock wrote on Tue, 10 Apr 2007

> Hi,
> 
> Not sure if this kind of modelling will throw OWL reasoners for a loop, 
> although I'm sure someone on this list will know. Is there a reason you can't 
> explicitly have a collection individual and a member_of_collection style 
> property that binds an instance to the collection?
> 
> For the case of a list, you can introduce a qua on the instance that stands 
> for the membership of the list. So,
> 
> array <-member_of- member -refers_to-> someIndividual
> 
> Where member has a property index, and index is set to be unique with respect 
> to the array instance, and the presence of a member with index x imples the 
> existance of a member with every index >=0 and < x. Alternatively, use a 
> linked list with e.g. a head/cons pair of relations and cardinality 
> restrictions to prevent unintended branching.
> 
> Using collection instances like this you can restrict someIndividual to a 
> specific class by placing a universal restriction on the inverse of member_of 
> that places a universal restriction to revers_to on that class. So:
> 
> PersonArray == Array &
>   all inverse(member_of) all refers_to Person
> 
> The member qua instances tend to be useful places to hang other things than 
> the index from, if the individual at that index in the list needs treating 
> differently to the individual at other indexes or independent of the list.
> 
> Sorry if you've been up and down this kind of solution already.
> 
> Matthew
Received on Wednesday, 11 April 2007 20:44:26 GMT

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