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Re: Draft for a "minimal dataset semantics"

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Fri, 14 Sep 2012 10:33:02 -0400
Message-ID: <5053401E.50703@gmail.com>
To: Antoine Zimmermann <antoine.zimmermann@emse.fr>
CC: RDF WG <public-rdf-wg@w3.org>

On 09/14/2012 09:26 AM, Antoine Zimmermann wrote:
>
>
> Le 13/09/2012 20:13, Peter F. Patel-Schneider a écrit :
>>
>> On 09/13/2012 12:50 PM, Antoine Zimmermann wrote:
>>> Le 13/09/2012 03:08, Peter F. Patel-Schneider a écrit :
>>>
>> [...]
>>
>>>>
>>>> It is also the case that an inconsistent default graph makes the named
>>>> graphs irrelevant.
>>>
>>> It makes the dataset inconsistent, which is fortunate.
>>
>> I don't consider this to be particularly fortunate. Why should an
>> inconsistent default graph make the named graphs irrelevant? Why should
>> the default graph situation bleed into the named graphs at all?
>
> This semantics consider that datasets are sentences and quotes of sentences 
> (not quote in the sense of Sandro's "quoting semantics, but in the usual 
> conversation sense). For instance, consider the following statements:
>
> Joe is a person. Joe is not a person. Joe told me "I am person".
>
> This is inconsistent. However:
>
> Joe is a person. Joe told "I am a person and I am not a person".
>
> This is consistent. What Joe says is inconsistent, but it's irrelevant for 
> the consistency of my statements.
>
This is a particular view of how RDF datasets should work.  I don't subscribe 
to this view.

>
>>>> This last is, I think, a particularly strong point against providing
>>>> this sort of semantics at all.
>>>
>>> By "this last", what do you mean? This last test case (T14.1) or this
>>> last sentence that you wrote above?
>>>
>>> I think you mean the former (if it's the latter, I don't see why). Do
>>> you think that, if the graphs--named and default--were independent, it
>>> would be acceptable? That's the alternative proposal where IGEXT maps
>>> IRIs to graphs, instead of resources to graphs.
>>
>> I prefer having the named graphs independent of each other, and
>> independent of the default graph. I might be able to live with the
>> situation where an inconsistent default graph makes the named graphs
>> irrelevant, but why should I have to? We could just go back to the
>> proposals from much earlier where these sorts of issues do not arise.
>
> Which proposals?
>

Here are some documents/messages with proposals.

http://www.w3.org/2011/rdf-wg/wiki/images/3/3b/Rdfwg-graphs-tf-report.pdf 
slide 5 proposal (a), although I can't find a separate source for the proposal 
itself

http://lists.w3.org/Archives/Public/public-rdf-wg/2012Mar/0041.html proposes a 
simpler semantics, which I prefer over the more complex one, but I prefer 
something even simpler

http://lists.w3.org/Archives/Public/public-rdf-wg/2012Apr/0188.html

http://lists.w3.org/Archives/Public/public-rdf-wg/2012Aug/0030.html the 
suggestion near the bottom of the message

>>
>> peter
>>
>> PS: Here is a reiteration of the old proposals.
>>
>> There is no independent notion of interpretations of RDF datasets. If
>> you want to do something like entailment between RDF datasets you can
>> either look at one component of the dataset, so you ask whether the
>> default graphs sit in an entailment relationship or ask whether the
>> graphs with a particular name sit in an entailment relationship, or you
>> can look at the entire dataset, so you ask whether the default graphs
>> sit in an entailment relationship and all the similarly-named graphs sit
>> in an entailment relationship. In each case you probably want to
>> consider a missing named graph to be the empty graph. This ends up being
>> more flexible and considerably simpler than the minimal semantics
>> currently being proposed, as well as requiring no new reasoning machinery.
>>
>
>
> To me, it is important to have entailment between datasets.
>
> { <n,G> }  entails  { <n,G'> }
>
> is not the same as "extract G from <n,G>, G entails G'".
>
> I want that the inferred triples are labeled by the graph IRI, for various 
> purposes including version management, provenance management, temporal 
> validity, etc.
>
I don't see what you get from this beyond entailment between RDF graphs.  If, 
however, the WG ends up with some definition of entailment between RDF 
datasets, I much prefer a direct relationship between the IRI and the graph.

peter
Received on Friday, 14 September 2012 14:33:36 GMT

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