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Re: Islands (ACTION-148)

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Tue, 28 Feb 2012 18:39:59 +0100
Message-ID: <4F4D116F.5050601@emse.fr>
To: public-rdf-wg@w3.org


Le 28/02/2012 16:36, Pat Hayes a écrit :
>
> On Feb 28, 2012, at 3:45 AM, Ivan Herman wrote:
>
>> Pat,
>>
>> I need explanation, 'cause I am lost, I am not ashamed to say
>> that...
>>
>>
>> On Feb 27, 2012, at 22:42 , Pat Hayes wrote: [snip]
>>>
>>>>
>>>> The use of a URI for a graph label in two different trig
>>>> documents should mean the same thing but combining two
>>>> datasets, like combining two graphs, will involve an
>>>> application deciding that is can be done.
>>>
>>> But how will it? ANY two graphs are semantically consistent, on
>>> this account,
>>
>> If my understanding of [2] is correct, each graph must be,
>> individually, consistent according to the RDF Semantics, ie, has to
>> have a proper model. The models may be different for two different
>> graphs with different labels, but I do not understand what you
>> say...
>
> I should have said, any two graphs are consistent *with one another*.

That's true about simple entailment and RDF entailment, but not in the 
proposal of [2] because, again, [2] does not say anything about the 
relationships between RDF graphs. It's all about the semantics of 
*datasets*, which are sets of pairs, not sets of triples.

> Put another way, there cannot be an inconsistency between something
> said on one graph and something said in a different graph. For
> example, suppose one graph says that :Joe :age '10'^^xsd:number and
> another graph says that :Joe :age '33'^xsd:number and a third graph
> says (in OWL) that :age is a functional property. Something wrong
> here, right? But no, not according to the proposed semantics. Put
> these three graphs into a single trig document, and this document has
> an interpretation, so it is consistent. So there is no inconsistency
> to be resolved: everything is fine, according to this semantics.

Put these three triples into a single RDF document and you have an RDF 
model, so it's consistent. If you rely on extensions of the RDF 
semantics, then I can certainly propose a number of extensions to [2] to 
deal with the specific use cases (which is what I want to provide in a 
future email).

>
>>> and two graphs (with different labels) NEVER entail any graph
>>> larger than either of them (such as their merge, for example),
>>> according to the semantics in [2].
>>
>> Again, I do not understand why. If two graphs have the same label,
>> then their merge, with the same label, is entailed, again by [2].
>
> With the same label, yes. I said, two graphs with different labels.

The label is key here. Of course, if you force the labels to be always 
different, you have problems. But this is not enforced by the semantics.

> If I put two copies of a graph into a single trig document with two
> different lables, one of the copies does not entail the other, even
> though they are the same graph.

Again, no, the RDF graphs entail each others. It's the pairs (n1,g), 
(n2,g) that do not entail each others. Which is exactly what I would 
like to have. Otherwise, I would not have made two copies in the first 
place.


AZ

>
> Pat
>
>>
>> Ivan
>>
>>
>>
>>> So all semantic relationships are reduced to triviality, so there
>>> can be no criteria available to check for acceptability on any
>>> semantic grounds. Remember, *every* URI might mean sometjhing
>>> completely different in another graph, so you can't say things
>>> like one graph says that x:joe is age 10 and the other says he is
>>> age 12: that URI might refer to Joe in one graph and Susan in the
>>> other, and the URI for the age property might mean age in one
>>> graph and being-a-handle-of in the other. Graphs become black
>>> holes of meaning, without any way for anything inside to
>>> influence or connect with anything outside.
>>>
>>>>
>>>> Islands aren't named or formally recognized - and one apps view
>>>> of "usable together" may not be the same as another apps.
>>>
>>> Oh what a tangled Web we weave.... (Sorry, couldnt resist :-)
>>>
>>> Pat
>>>
>>>>
>>>> Andy
>>>>
>>>> [1] http://www.bbc.co.uk/doctorwho/dw [2]
>>>> http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/RDF-Datasets-Proposal
>>>>
>>>>
>>>
>>>
>>>>
------------------------------------------------------------
>>> IHMC                                     (850)434 8903 or
>>> (650)494 3973 40 South Alcaniz St.           (850)202 4416
>>> office Pensacola                            (850)202 4440   fax
>>> FL 32502                              (850)291 0667   mobile
>>> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> ---- Ivan Herman, W3C Semantic Web Activity Lead Home:
>> http://www.w3.org/People/Ivan/ mobile: +31-641044153 FOAF:
>> http://www.ivan-herman.net/foaf.rdf
>>
>>
>>
>>
>>
>
> ------------------------------------------------------------ IHMC
> (850)434 8903 or (650)494 3973 40 South Alcaniz St.
> (850)202 4416   office Pensacola                            (850)202
> 4440   fax FL 32502                              (850)291 0667
> mobile phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>
>
>
>
>
>
>

-- 
Antoine Zimmermann
ISCOD / LSTI - Institut Henri Fayol
École Nationale Supérieure des Mines de Saint-Étienne
158 cours Fauriel
42023 Saint-Étienne Cedex 2
France
Tél:+33(0)4 77 42 83 36
Fax:+33(0)4 77 42 66 66
http://zimmer.aprilfoolsreview.com/
Received on Tuesday, 28 February 2012 17:40:08 UTC

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