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RE: lightweight reification (was Representing trust (and other co ntex t) in RDF)

From: McBride, Brian <bwm@hplb.hpl.hp.com>
Date: Mon, 29 May 2000 10:27:51 +0100
Message-ID: <5E13A1874524D411A876006008CD059F23924A@0-mail-1.hpl.hp.com>
To: "'Pierre-Antoine CHAMPIN'" <champin@bat710.univ-lyon1.fr>
Cc: RDF interest group <www-rdf-interest@w3.org>
Pierre,

>"McBride, Brian" wrote:
>> M&S is quite specific when it talks about reification that a
>statement and the resource that models it are different
>things.  I haven't understood why (...)
>
>what M&S is saying is that asserting a reified statement is
>*not* asserting the statement itself,
>which means that you can talk about a statement without "believing" it.
>

I appreciated the need for this, but hadn't understood thats what those
words in the m&s spec meant.  Thanks for the clarification.

I wasn't going to put this next bit out but as its apposite to the point you
just made ...

It had occurred to me a little while back that there was a concept implied
in the model and syntax document, but not addressed explicitly in it.

When we talk about RDF models or RDF serializations, there is an implied
container that the specs don't talk about.  So when we write a model like:

    [subject1] ---[predicate 1]---> [object1]
    [subject2] ---[predicate 2]---> [object2]

There is an implied 'model' or StatementSet of which these statements are a
member.  This is a concept that is clearly present in Sergey's API.  Each of
these statements has the implied 'property' that it is a member of a model.

It is useful to be able to assign a URI to a model so that it can be
identified and so that statements may be made about the collection.  This
might be represented as:

   +--Model------------------------------------+
   |                                           |
   |   [subject1]---[predicate 1]--->[object1] |
   |   [subject2]---[predicate 2]--->[object2] |
   |   [Model]---[asserted by]--->[Brian]      |
   +-------------------------------------------+

Again this is what Sergey has proposed, though I think there are
alternatives to digest URI's to identify the model.

This is certainly useful when building a large repository.

When statements are treated as resources, there can be models of the form:

        +--[subject]--[predicate]-->[object]
        |
        |
   +----|--Model-------------------------------+
   |   \ /                                     |
   |   [subject1]---[predicate 1]--->[object1] |
   |   [subject2]---[predicate 2]--->[object2] |
   |   [Model]---[asserted by]--->[Brian]      |
   +-------------------------------------------+

which is intended to indicate that subject1 is the statement outside of the
Model.  Thus a model can contain statements about a statement S, without
containing S itself.

At the time it also seemed this might provide a way of ducking metaphysical
issues of 'belief' and 'truth' and reducing them to statements about set
membership, but I really must go chase those pointers from Dan and Guha as
there has clearly been much deeper thinking about this than I have done.

Brian
Received on Monday, 29 May 2000 05:28:03 GMT

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