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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))

NOT:

   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.

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

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