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Re: [GRAPH] graph deadlock?

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Wed, 21 Dec 2011 11:15:21 +0000
Message-ID: <4EF1BFC9.9020401@epimorphics.com>
To: public-rdf-wg@w3.org


On 20/12/11 18:45, Pat Hayes wrote:
>
> On Dec 20, 2011, at 2:29 AM, Ivan Herman wrote:
>
>> Pat,
>>
>> On Dec 20, 2011, at 05:45 , Pat Hayes wrote:
>>
>> [skip]
>>
>>>
>>> Now, consider the case where a URI  UUU is used as a graph label in a dataset, and also occurs in the RDF inside a graph in that same dataset, where it is interpreted as denoting, say, a human being or a mailbox. OK so far. Now, however, add the dataset some more RDF (perhaps in the default graph used to express some metadata, for example) in which that same URI is intended to be used to refer to the graph that it labels. There are *no* RDF interpretations in which a single URIref can denote two different things. So this dataset as a whole has no satisfying interpretations. So it is formally inconsistent. Moreover, the inconsistency arises directly, and obviously, from this usage in which a URI is used to "name" something other than what everyone agrees it is in fact interpreted to mean (as, vividly, in Ivan's example using an email address). And this is, surely, *obviously* at odds with the basic assumption of the entire Web, that URIs, when considered as names, identify
 *one* thing.
>>>
>>
>> is 'labeling' and 'identifying' the same?
>
> Well, maybe not. But I suspect that if we try to say this, nobody will take the slightest notice. They certainly sound like they ought to be very closely related, so closely that only philosophers could distinguish them, and then only when there is an R in the month. And by the way, SPARQL talks about these URIs *naming* the graph, which sounds even more like identifying.
>
>> My non-semantics dataset view talks about labeling only. 'Indexing' may be another term.
>>
>> I come back to the quad store example. I do not believe that quad stores make any assumption, by default, to the behaviour of the URI-s in the 4th column, they are just 'there'.
>
> Fine. But when they also occur in the (say) 3rd position, do they or
do they not then mean the same as they meant when they occur in the
fourth position? (Or maybe: does what they mean in the 3rd position have
any relationship at all to their role while being-there in the fourth
position?) The answer seems to be, sometimes they do (of course) and
sometimes they don't (of course), but nothing records which case is
which. And I object to that situation, as it produces faux-RDF which is
designed to be systematically ambiguous in meaning. And we can blather
about "contexts" for ever, but until this notion is made reasonably
precise, all such talk is indeed just blather. I have been to several
workshops on 'contexts' where *every single speaker* had a different
notion of what the word 'context' meant.

I think they do (strictly, "they should do") mean the same thing which 
ever slot they are in.

If the IRI in the 4th slot is the graph container the graph (value) was 
obtained from, then use of the IRI in a triple denotes the graph container.

I'm not sure that anyone is suggesting standardising otherwise (please 
correct me here) - the 4th slot isn't directly "denotes" the graph but 
that IRI does denote something, and that something is in some 
relationship to the graph.

The only example where this is rather weak is the "primary topic" 
pattern and there one of the users has indicated they'd probably object 
to it being standardised anyway.

	Andy

>
> Pat
>
>>
>> Ivan
>>
>>
>>
>>
>>>>
>>>> When you say “this is illegal in RDF” then I think this has to be read as “I don't like it”.
>>>
>>> No, I mean it violates the semantic assumptions of the (normative) RDF model. I might suggest that when you say "It isnt illegal", this has to be read as "I havnt understood the semantics spec."
>>>
>>>>> We could simply declare that RDF has no semantics, and is simply to be used by programmers to mess around with in ways they find handy. Really, this might be the best way to move forward. But until we do this, we have to take the semantics seriously.
>>>>
>>>> Or we could just not bother giving any formal semantics to any new parts that are added to RDF. Several parts of RDF don't have a formal semantics and work pretty much fine anyways, e.g., RDF lists.
>>>
>>> They have no semantics because they dont need any semantics. If a list had a semantics, it would describe the list. Those are basically LISP S-expressions coded into RDF triples: they *exhibit* the required structure rather than *describe* it.
>>>
>>> But I agree, we could indeed not give semantics to new parts. The sticking point, however, is that this particular 'new' part is already using the 2004 RDF semantics, but it is using it incorrectly.
>>>
>>> Pat
>>>
>>>>
>>>> Best,
>>>> Richard
Received on Wednesday, 21 December 2011 11:15:49 GMT

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