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Re: Islands (ACTION-148)

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 28 Feb 2012 09:36:41 -0600
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, RDF-WG <public-rdf-wg@w3.org>
Message-Id: <AF41437E-39B1-41A1-BC0C-46449983CC51@ihmc.us>
To: Ivan Herman <ivan@w3.org>

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*. 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. 

>> 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. 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. 

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
>>> 
>>> 
>> 
>> ------------------------------------------------------------
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>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> ----
> 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
Received on Tuesday, 28 February 2012 15:37:17 UTC

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