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Re: summary of 'a triple is not unique' and 'statements/reified' statements

From: Graham Klyne <GK@Dial.pipex.com>
Date: Wed, 29 Nov 2000 20:17:02 +0000
Message-Id: <>
To: Libby Miller <Libby.Miller@bristol.ac.uk>
Cc: www-rdf-interest@w3c.org
At 02:46 PM 11/28/00 +0000, Libby Miller wrote:

>Hi all,
>I've been following the threads about statements with interest, and I've
>had a go at summarising them. There's a document at


this is a useful attempt on a difficult subject.  By "difficult", I mean 
that there are clearly many subtleties that cause different people to see 
things differently -- it all seems quite simple to me ... for today at 
least ;-)

I think my earlier message 
which you cite, captures my view.  Based on that, I have some comments on 
your interpretation:

>1. 'reified statements are statings'
>Jonas Liljegren, Seth Russell(?), Graham Klyne, Pierre-Antoine Champin, 
>Jonathan Borden
>On this view, although a reified statement represents a statement, it is 
>only one possible representation of it. There is therefore not
>necessarily a one-to-one correspondence between a statement and its 
>reification (Graham Klyne).


>Statements may or may not be unique (there seems to be a preference for 
>uniqueness, in some sense, maybe within a context (space) or
>model). Introduction of spaces: Jonathan Borden.

The RDF model seems to say that statements are unique.  Contexts don't 
change this.

>This means that reified statements should be regarded as unique of 
>themselves and as statings. Each stating is unique. If someone else makes
>a reified statement with the same subject, predicate and object 
>properties, then we cannot regard that stating as being the same as the first.
>The loss of information that occurs in Liljegren's example would not occur.

Here, I differ slightly:  IMO, uniqueness of a reification depends entirely 
on the URI that identifies the statement resource; i.e. the 'r' in:

    [ ]--rdf:predicate-->[p]
    [ ]--rdf:subject---->[s]
    [ ]--rdf:object----->[o]

If one document or context makes an assertion about the statement [r], and 
some other document makes a different assertion using the same URI for [r], 
then they are assertions about the *same* stating, even though the 
reification is invoked in very different places.

>However, when a reified statement is given a URI via the ID attribute then 
>this implies that any reified statement with that URI is referring to
>the same stating.


>      loss of some information, because the distinction between the 
> statement and the stating is being lost, so that we are removing the
>      possibility of aggregation of this part of the data.

I don't agree with this.  The distinction still exists.  The fact that the 
statement is an abstraction that is not directly represented in RDF does 
not remove the distinction.

[As I write this, I think I see one of the misunderstandings...]

Reification should NOT be regarded as synonymous with 
"stating".  Reification is the mechanism we have to create a resource that 
models a statement;  asserting that a statement was stated in some context 
(i.e. describing a "stating") is just one thing we can do with a reification:

    [  ]--rdf:subject---->[Foo]
    [  ]--rdf:predicate-->[heightInMillimetres]
    [  ]--rdf:object----->"25.4"
    [  ]--statedBy------->[Somebody]

But, we might alternatively wish to assert that two statements are 
equivalent, without asserting the truth of either, or even asserting that 
anybody made such a claim (stating):

    [  ]--rdf:subject---->[Foo]
    [  ]--rdf:predicate-->[heightInMillimetres]
    [  ]--rdf:object----->"25.4"

    [  ]--rdf:subject---->[Foo]
    [  ]--rdf:predicate-->[heightInInches]
    [  ]--rdf:object----->"1"


To reiterate:  the second example uses above reifications of two (abstract) 
RDF statements to make the assertion that the statements are 
equivalent.  Neither of these reifications are "statings".


Graham Klyne
Received on Wednesday, 29 November 2000 16:07:39 UTC

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