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Re: plural vs singular properties (a proposal)

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Sat, 5 Jan 2008 22:29:11 +0000
Message-Id: <17404A4E-5971-4C93-9938-65CA86DB8976@cs.man.ac.uk>
Cc: SW-forum Web <semantic-web@w3.org>
To: Garret Wilson <garret@globalmentor.com>

On Jan 5, 2008, at 3:16 PM, 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.

It's not a conflict. consider the following table version (let's give  
the blank node an indentifier, ex:foo; blank nodes *are* a departure,  
but one well handled by "naive" tables or "codd" tables as they are  
known in the literature). First row are the column headers:

ID            dc:subject
ex:foo     semantic web
ex:foo     database

This a perfectly fine relational table (to be a bit loose in  
terminology). What wouldn't be is:

ID            dc:subject
ex:foo     semantic web
ex:foo     semantic web
ex:foo     database

Since this is a bag not a set. In SQL systems, you do have to deal  
with the fact of bags (hence the keyword DISTINCT).

So, short answer: This isn't a *duplicate* row. It's two rows.

Cheers,
Bijan.
Received on Saturday, 5 January 2008 22:29:25 GMT

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