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Re: rdfs:Graph ? comment on http://www.w3.org/TR/rdf11-concepts/#section-dataset and issue 35

From: David Booth <david@dbooth.org>
Date: Thu, 12 Sep 2013 00:33:38 -0400
Message-ID: <52314422.1000703@dbooth.org>
To: Pat Hayes <phayes@ihmc.us>
CC: Jeremy J Carroll <jjc@syapse.com>, Sandro Hawke <sandro@w3.org>, "public-rdf-comments@w3.org Comments" <public-rdf-comments@w3.org>, www-archive <www-archive@w3.org>
[Let's move this discussion to www-archive@w3.org please, as it isn't 
relevant to Jeremy's comment.  All follow-ups there please.]

On 09/11/2013 10:32 PM, Pat Hayes wrote:
> On Sep 11, 2013, at 5:38 PM, David Booth wrote:
>> On 09/09/2013 02:51 AM, Pat Hayes wrote:
>>> The question though is, whether
>>> I(<http://my.graph.name.example.org/>) = the graph you want it
>>> to mean. The problem is that there are people who want to use an
>>> IRI to simultaneously denote a person (say) but also be the name
>>> of a graph (eg of information about that person). And they have
>>> deployed systems and much money vested in being able to do this.
>> Uh . . . this may be opening up a can of worms, but what you're
>> saying sounds a lot like the IRI resource identity ambiguity issue
>> that has been discussed quite a lot in the past.  In short, there
>> is no conflict if either: (a) the class of persons has not been
>> asserted to be disjoint with the class of graphs
> Indeed. I am assuming throughout this discussion that graphs and
> persons are disjoint classes, and that this is known by all parties
> involved.

Okay, but not all software needs to make that distinction.  So unless it 
has been explicitly stated in the graph (or implied as a valid entailment)

>> ; or (b) the IRI denotes a person in one RDF interpretation (e.g.
>> in one system) but denotes a graph in a different RDF
>> interpretation (e.g. in a different system).
> That is nonsense, as I have explained to you many times in the past.

Baloney!  *Each* interpretation maps an IRI to one resource, but **RDF 
ALLOWS MULTIPLE INTERPRETATIONS**!  And different interpretations can 
perfectly well map the same IRI to different resources.  Please stop 
trying to look at RDF in terms of only one interpretation!  That is 
*not* the only way -- or the only correct way -- to think about RDF.

> Interpretations are not systems: they are alternative ways to
> construe what IRIs denote.

Yes, and different systems (or people) can and do construe them differently.

> But each IRI denotes one thing, in all
> possible interpretations.

No, in *each* possible interpretation, not in *all* possible 
interpretations.  I.e.,

   For any interpretation I and URIs U1 and U2,
   (U1=U2) => (I(U1) = I(U1))


   For any interpretations II and I2, and URIs U1 and U2,
   (U1=U2) => (I1(U1) = I2(U2))

I.e., the uniqueness does not hold *across* interpretations.  It only 
holds within *each* interpretation individually.

> (The current RDF 1.1 semantics socument
> makes thie very explicit, by the way.)

Yes, I noticed that, and the current wording is *incorrect*.  It needs 
to be fixed, as it wrongly implies that RDF may only be viewed from the 
perspective of a single RDF interpretation, and that is simply *wrong*. 
  I have not yet raised that issue, but I will.  I wanted to talk it 
over with you first, before causing a long email thread.

> If we want to allow different
> occurences of an IRI to denote different things, then we would need
> some kind of context mechanism in RDF, which it currently does not
> have, and providing which would have been beyond this WGs charter.

You are talking about something entirely different than what I am 
talking about.  I am not and never have been talking about that kind of 
notion of context.  I am talking about the *existing* RDF Semantics, BUT 
from the perspective of looking at the set of satisfying interpretations 
for an RDF graph -- not from the perspective of a single interpretation.

>> I don't know if this observation would help resolve the problem
>> that you're mentioning though.
> Neither of them do, I'm afraid.

Okay.  I don't know enough about the graph naming debate that you 
mentioned to know if it was relevant, so I'll take your word for it.

Received on Thursday, 12 September 2013 04:34:06 UTC

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