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Re: Are duplicate property/value pairs permitted for a resource?

From: David Hyatt <hyatt@netscape.com>
Date: Thu, 08 Apr 1999 11:29:18 -0700
Message-ID: <370CF57E.598855DA@netscape.com>
To: Dan Brickley <Daniel.Brickley@bristol.ac.uk>
CC: Samuel Yang <syang@peoplemoverinc.com>, "'www-rdf-comments@w3.org'" <www-rdf-comments@w3.org>, "'rdf-dev@mailbase.ac.uk'" <rdf-dev@mailbase.ac.uk>
Oops. I misread the original question and therefore answered it incorrectly.  I
thought he was asking if you could have multiple assertions to different targets
using the same property (e..g, (pred, sub, obj1), (pred, sub, obj2)...), when he was
really asking if you could have multiple assertions to identical targets using the
same property.

Dave
(hyatt@netscape.com)

Dan Brickley wrote:

> The broad answer to this is implied by RDF's formal model,
> http://www.w3.org/TR/REC-rdf-syntax/#model
>
>            1.There is a set called Resources.
>            2.There is a set called Literals.
>            3.There is a subset of Resources called Properties.
>            4.There is a set called Statements, each element of which is a triple
>         of the form
>
>              {pred, sub, obj}
>
>         Where pred is a property (member of Properties), sub is a resource
>         (member of Resources), and obj is either a resource or a literal
>         (member of Literals).
>
> Since a collection of facts in RDF is a set of statements, and since any
> set by standard definition of the term can't contain the same element twice,
> multiple identical members of the set 'Statements' cannot exist in any
> given RDF model. The only complication is regarding literals.
> My understanding is that there is no notion of numerical identity of
> literals, ie. two strings being one-and-the-same literal. Consequently,
> two assertions with the same resource and property _and_ the same
> string literal, eg "Smith", will correspond to two _different_ members
> of the set 'Statements'.  (If I'm right this should go in a FAQ... ;-)
>
> Quite what this means in terms of processor behaviour depends on your
> application. The spec just defines the data model.
>
> Dan
>
> On Thu, 8 Apr 1999, Samuel Yang wrote:
>
> > I'm sending this query out again to a wider audience...  Anybody have an
> > answer?
> >
> > -----Original Message-----
> > From: Samuel Yang [mailto:syang@peoplemoverinc.com]
> > Sent: Friday, April 02, 1999 12:31 PM
> > To: 'www-rdf-comments@w3.org'
> > Subject: Are duplicate property/value pairs permitted for a resource?
> >
> >
> > If an RDF processor is asked to add a property/value pair for a resource,
> > but that property/value pair already exists for that resource, should the
> > processor:
> >
> > (a) Add a duplicate property/value pair to the resource, or
> > (b) Ignore the "new" property/value pair?
> >
> > I couldn't find anything in the spec regarding this issue.  The closest
> > thing I found had to do with fact that the Bag and Seq containers allow
> > multiple instances of the same value.  However, that isn't even the same
> > issue, since items within a collection have unique property names (rdf:_1,
> > rdf:_2, etc.)
> >
> > Samuel C. Yang
> > syang@peoplemoverinc.com
> >  <<Samuel C. Yang.vcf>>
> >
> >
Received on Thursday, 8 April 1999 14:30:21 GMT

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