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Re: comment on N-ary relations draft

From: Guus Schreiber <schreiber@cs.vu.nl>
Date: Wed, 08 Dec 2004 04:07:23 +0100
Message-ID: <41B66FEB.8070403@cs.vu.nl>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: public-swbp-wg@w3.org, joint-committee@daml.org

Peter F. Patel-Schneider wrote:

> I just read the N-ary relations draft and I am somewhat confused as to why
> it has the two representation patterns.  I don't see that the two patterns
> are different in any substantial way as the only difference between them is
> the direction of one arrow.  This difference may matter in some formalisms
> but doesn't in RDF/RDFS (as they are too weak to notice much difference) or
> OWL (as it has the inverse construct).
> So, my question is why maintain the two different representation patterns?

Peter, thanks very much for the comment.

Natasha and Alan are probably the best people to answer this, but I will 
give you my reading of the difference.

The distinction is of a modelling nature. In Pattern 1 you create a 
helper relation (represented as a class) which has (in most cases) no 
name in the domain of interest. In Pattern 2 the relation class has some 
name in the domain, typically a noun representing some activity (e.g. 
purchase, enrolment, transaction, subscription). I think this is an 
important difference of which developers should be aware. In particular, 
in the case of pattern 1 a an engineer might find it weird to construct 
a name from the blue, and it may help her/him to know it's actually good 
practice. The resulting representation is very similar, I agree. Maybe 
we should make this point more clear in the text.

Hope this helps,


> Peter F. Patel-Schneider
> Bell Labs Research

Free University Amsterdam, Computer Science
De Boelelaan 1081a, 1081 HV Amsterdam, The Netherlands
Tel: +31 20 444 7739/7718
E-mail: schreiber@cs.vu.nl
Home page: http://www.cs.vu.nl/~guus/
Received on Wednesday, 8 December 2004 03:07:39 UTC

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