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Re: three kinds of dataset

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 6 Mar 2012 13:44:17 -0600
Cc: public-rdf-wg@w3.org
Message-Id: <5216BD3A-D9CE-49AF-A512-BEEF66F5C423@ihmc.us>
To: Peter F. Patel-Schneider <pfpschneider@gmail.com>

On Mar 6, 2012, at 12:43 PM, Peter F. Patel-Schneider wrote:

> From: Pat Hayes <phayes@ihmc.us>
> Subject: Re: three kinds of dataset
> Date: Tue, 6 Mar 2012 12:30:13 -0600
> 
>> A few quick clarifications.
>> 
>> On Mar 6, 2012, at 11:30 AM, Peter F. Patel-Schneider wrote:
>> 
>>> From: Pat Hayes <phayes@ihmc.us>
>>> Subject: three kinds of dataset
>>> Date: Tue, 6 Mar 2012 00:55:58 -0600
> 
> [...]
> 
>>>> Case 3. The graph labels in a dataset are understood to be actual names
>>>> of the graph they are associated with, ie to formally denote the graph,
>>>> so that when used in RDF these labels refer to the actual graph. (Or
>>>> maybe, to some larger graph of which the graph indicated is a part.) The
>>>> labelled graphs are then essentially being mentioned rather than used,
>>>> so that the dataset can be asserted without in any way asserting the
>>>> component named graphs it contains. These named graphs are more like
>>>> graph literals than a graph in an RDF graph document.  (There is also
>>>> the idea that the label actually names a graph container whose state is
>>>> initially the graph shown, and no doubt other variations on this theme
>>>> are possible; let me lump all these together for now.)
>>> 
>>> It appears that the essence here is that there is a new datatype,
>>> RDFGRAPH, whose literals are RDF graphs.
>> 
>> Well, that is one way to do it. I like the proposal in Bizer et
>>> al. better, myself.  
>> 
>>> It may even be that the
>>> graph-subset relationship is exposed in RDF (to allow partial
>>> specification of the graph).  However, there is no notion that the
>>> elements of this datatype carry RDF semantics.
>> 
>> No, that is exactly what is proposed. The RDF graphs being named here
>> are real RDF graphs with RDF semantics. But the dataset names them
>> rather than asserts them.  
> 
> What aspects of the RDF semantics percolate up here?  If none, then the
> domain elements should just be RDF graphs, as graphs.  if some, then
> just exactly what?

Yes, they are RDF graphs, as graphs. But to say this is not to say that they have no semantics. If they get imported into another graph, they have the same semantics they would have if they had never been in the dataset. I just wanted to distinguish this aspect from case 2 (which does change the meaning) and to emphasise that putting a graph in a graph literal does not eliminate its semantics altogether. 

> 
> [...]
> 
>>>> So, take Tim Lebo's example from David's recent email:
>>>> 
>>>>> :account_1 {
>>>>>   :entity a prov:Entity
>>>>> }
>>>>> 
>>>>> :account_2 {
>>>>>   :entity a prov:Activity
>>>>> }
>>>>> 
>>>>> prov:Entity owl:disjointWith prov:Activity .
>>>> 
>>>> and presume that we are accepting OWL semantics. 
>>> 
>>>> Case 1 says: yes, these
>>>> three are OWL-inconsistent taken together. (Of course it allows that you
>>>> might not want to take them together, perhaps even that you should not
>>>> take them together, but as far as what they mean, they are indeed
>>>> mutually inconsistent.)  
>>> 
>>> Huh?  Case 1 appears to say that this is just an RDF datastructure, with
>>> no semantics, and therefore inconsistency is not an issue.
>> 
>> Why would an RDF datastructure have no semantics? The RDF semantics is
>> normative for RDF. Maybe consistency isnt something anyone is
>> worried about, for pragmatic reasons of some kind, but that does not
>> alter the fact of the presence of the inconsistency in the data.  
> 
> Why should an RDF datastructure have any semantics (beyond its mapping
> into some abstract datatype)?
> 
> [...]
> 
> 
>>>  I'm not sure what is gained [in Case 3] over case 1,
>>> however. 
>> 
>> The ability to use the IRI graph labels inside RDF triples to refer to
>>> the graph, effectively using RDF as metadata.  
> 
> To what effect?  If none, then there is no reason to do it.
> 
> [...]
> 
>>> If I understand what is going on here, Pat's proposal for case 2 is a
>>> kind of situation calculus whereas Antoine's is a kind of modal logic.
>> 
>> Nicely put. Actually I think Antoine's is a very simple hybrid logic
>> which has labels for the possible worlds, rather than a modality. But
>> whatever.  
>> 
>>> These are both ways of extending RDF.  I would *not* say that Antoine's
>>> is an un-extension of the RDF semantics.  
>> 
>> My point was just that under Antoine's construction, a dataset has a
>> *weaker* meaning than it would if we applied the straighforward 2004
>> semantics to all its graphs.  
> 
> And so, also, in the situation calculus version, I believe.
'
Measured in actual entailments, yes you are right. 

Pat

> 
> [...]
> 
> peter
> 
> 

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Received on Tuesday, 6 March 2012 19:44:49 GMT

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