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Re: plural vs singular properties (a proposal)

From: Frank Manola <fmanola@acm.org>
Date: Sat, 5 Jan 2008 11:11:56 -0500
Message-Id: <F12ECEF9-0506-49F3-8545-2C2B9E201F72@acm.org>
Cc: SWIG <semantic-web@w3.org>
To: Garret Wilson <garret@globalmentor.com>


Assuming I understand what you're talking about, this *isn't* a  
conflict with the relational model.  To flesh out your example a bit,  
suppose you have a paper, book, or article, and want to record  
subject descriptors.  Likely there would be multiple values for  
"subject", and your relation to represent that would be

Subject(publicationID, value)

with tuples like (12345 is the publication identifier): <12345,  
semantic web>, <12345, database>, etc.

The relational model (the theory, not the practice) rules out  
duplicate tuples in the same relation, but you'll note these are not  
duplicate tuples.  The corresponding triples would be subject(12345,  
semantic web), subject(12345, database), etc. (substitute some bNode  
identifier or URI for 12345 in these RDF examples)  These aren't  
duplicate tuples either;  it's just that the RDF predicate (which  
corresponds to the relation name in the relational model) is  
repeated.  But that's just notation, it doesn't change the meaning.

More generally, RDF *is* a relational model;  one that restricts  
itself to binary relations, and in some other ways.


On Jan 5, 2008, at 10:16 AM, Garret Wilson wrote:

> Garret Wilson wrote:
>> How does RDF justify repeated properties?
> Sorry, maybe I would have been clearer if I would have said,  
> "multivalued properties", in which a property appears multiple  
> times for the same resource but with different values, e.g.
> <rdf:Description>
>  <dc:subject>semantic web</dc:subject>
>  <dc:subject>database</dc:subject>
> </rdf:Description>
> This is an area of conflict with the relational model, and I'm  
> wondering how RDF justifies this.
> Thanks,
> Garret
Received on Saturday, 5 January 2008 16:13:18 UTC

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