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Re: Repeated properties versus Bags [Was: New public version of RDF Model and Syntax Draft Specification]

From: Ralph R. Swick <swick@w3.org>
Date: Tue, 28 Jul 1998 10:03:49 -0400
Message-Id: <3.0.5.32.19980728100349.00a22d60@127.0.0.1>
To: "Pasqualino \"Titto\" Assini" <assini@kamus.it>
Cc: www-rdf-comments@w3.org
At 12:42 AM 7/28/98 +0200, Pasqualino \"Titto\" Assini wrote:
http://lists.w3.org/Archives/Public/www-rdf-comments/1998JulSep/0011

>The accuracy and open mindness with which you evaluate external comments
>it's for me the best guarantee of the high quality of your work. 

Thank you for the compliment.  And thank you especially for taking
the time to review the draft specification and help us make it better.

>As the expressive power of the language wouldn't be compromised, as
>there is nothing that can be expressed with repeated values that
>couldn't be expressed with a Bag, I wonder why we shouldn't simply get
>rid of repetitions.

We considered doing exactly this; in fact, we started with a
design choice to disallow repeated properties.  But some of
our client applications felt that Bags were too cumbersome
for some common situations such as a work with multiple authors.

A second reason for not disallowing repeated properties in
the data model is the observation that there can in general
be multiple Descriptions of the same resource.  We do not
wish to hard-wire into the core of RDF a single mechanism
for conflict resolution (do we discard some properties if
they are repeated and if so, which one(s)?  do we discard
the entire Description?)

If, for example, two Descriptions give separate prices for
an item and one Description is further described by a
property saying "valid 1998-07-28 only", there is no useful
way the core RDF can know enough semantics to recognize
that there is no logical conflict.

So while I am very sympathetic to disallowing repeated
properties, I forsee further issues if we try to do so.

>As you perfectly know, in technical matters it's almost never required
>to find a new solution to a given problem but rather to operate a choice
>among the many existing solutions.
>
>Whatever goes in the direction of simplifing this choice it's a step in
>the right direction.  

I completely agree.  We need to find a solution that is "as simple
as possible but no simpler".  Thanks for continuing to help refine
our understanding of "as simple as possible".

>That's exactly why people will be drawn to RDF.
>
>They will like the fact that it offers a "pre-canned" semantic model
>that radically reduces the number of useless choices that they have to
>make to devise a semantic schema.

Great; I am very pleased that you see things going this way.

Regards,
-Ralph R. Swick
 W3C/MIT
Received on Tuesday, 28 July 1998 10:05:42 GMT

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