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RE: Proposed response for timbl-02 (reification semantics)

From: <Patrick.Stickler@nokia.com>
Date: Thu, 10 Apr 2003 15:33:49 +0300
Message-ID: <A03E60B17132A84F9B4BB5EEDE57957B01B90CBC@trebe006.europe.nokia.com>
To: <danbri@w3.org>
Cc: <Jan.Grant@bristol.ac.uk>, <bwm@hplb.hpl.hp.com>, <gk@ninebynine.org>, <w3c-rdfcore-wg@w3.org>




> > After thinking about this some more, I've realized that I don't have
> > a problem with the inference you suggested. I.e., I'm OK with
> > the following entailment
> > 
> > {
> >    _:s a rdf:Statement .
> >    _:s rdf:subject <s1> .
> >    _:s rdf:predicate <p1> .
> >    _:s rdf:object <o1> .
> >    _:s #source #x .
> >    <s1> owl:sameIndividual <s2> .
> >    <p1> owl:sameIndividual <p2> .
> >    <o1> owl:sameIndividual <o2> .
> > }
> > log:implies
> > {
> >    _:s a rdf:Statement .
> >    _:s rdf:subject <s2> .
> >    _:s rdf:predicate <p2> .
> >    _:s rdf:object <o2> .
> >    _:s #source #x .
> > }
> > 
> > because reification, as now defined, is not quoting. 
> 
> Ah, ok, that makes things simpler. My previous mail was 
> written in concern that
> you somehow wanted to block this inference from going through.

Right. Sorry for the confusion. Thirty lashes for me for trying
to answer email and participate in a meeting at the same time ;-)

If only I could multitask like Linux... ;-)

> > If we add verbage of any kind, then it should be to the effect
> > that such entailments hold.
> 
> OK. Patrick, hope you don't mind us picking on you as a 
> sample user of 
> rdf reification, but let's follow this one through a bit further.

Pick away.

> Your current defintion for 'source' is as follows:
> 
>       <rdfs:Property rdf:about="&rdfx;/source">
>          <rdfs:comment>An RDF schema in which the statement
> occurs.</rdfs:comment>
>          <rdfs:domain rdf:resource="&rdf;#Statement"/>
>          <rdfs:range rdf:resource="&rdfx;/Schema"/>
>       </rdfs:Property>
> 
> This (sorry jang)
> 'strongly suggests'
> 'seems to me to be saying'
> 'leads me as an implementor to believe'
> 
> that because of 
> 
> >    _:s a rdf:Statement .
> >    _:s rdf:subject <s2> .
> >    _:s rdf:predicate <p2> .
> >    _:s rdf:object <o2> .
> >    _:s #source #x .
> 
> the RDF statement
> 
> <s2> <p2> <o2> .
> 
> ...occurs in the RDF schema referenced.

Insofar as what that statement is saying, yes. But not
necessarily in that particular form. I.e. all of the 
following are synonymous:

  <s1> <p1> <o1> .
  <s1> <p2> <o1> .
  <s1> <p1> <o2> .
  <s2> <p1> <o2> .
  ...

and it is quite true that the source denoted by #x expresses
the assertion that any of those synonymous permutations
of that assertion.

Since reification is not quoting, everything is fine, and
the entailments based on the owl:sameIndividualAs assertions
do not "make" the source say something it has not. It *has*
said

  <s2> <p2> <o2> .

even if it hasn't used those URIrefs to say it.

The inferences are not "putting words into the schemas's mouth".

> Now you don't formally define 'occurs' here.  
> For the sake of our example scenario, let us assume that 
> <s2>, <p2> and
> <o2> URIrefs are not anywhere to be found in the RDF document that
> the 'source' property references.

Fine. So what.

> The work of our health warning is to help RDF vocabulary creators use
> language in their defintions for properties such as this which won't
> raise inaccurate expectations. 

Exactly. So long as they understand that reification is not quoting,
and that any free variation of synonymous URIs does not make the
source say anything new, then they will have grokked reification as
now defined.

> In this case, an inaccurate 
> expedtation 
> would be that the URIs <s2>, <p2> and <o2> are labels on a triple 
> from the graph serialized in the RDF schema document 
> referenced by the 
> source property. (or some refinement of that; it's hard to 
> word this stuff)
> 
> Does that seem correct? ie. that words like 'occurs' in this context
> are super-slippery... 

'Expressed' may be better than 'occurs'. I think the key distinction
to be made in the specs is that reification captures what is
asserted, not necessarily how it is asserted. I.e., whatever the synonymous
<*1> and <*2> URIrefs denote, what matters is what is being asserted about the
resources denoted, not the specific URIrefs being used to assert it.

Right?

Patrick
Received on Thursday, 10 April 2003 08:33:55 EDT

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