Re: datasets mean their default graphs?

On 20/06/13 16:34, Markus Lanthaler wrote:
> On Thursday, June 20, 2013 1:28 PM, Andy Seaborne wrote:
>> On 20/06/13 07:43, Pat Hayes wrote:
>>> Have we agreed on Sandro's idea for the meaning of a datastore to be
>>> that of its default graph? I would like to add this paragraph to
>>> Semantics, section 10:
>
> I think we have:
> https://www.w3.org/2013/meeting/rdf-wg/2013-06-12#resolution_1
>
>
>>> <p>If a dataset is published as an assertion then it MUST be
>>> interpreted to be an assertion of its default graph. Semantic
>>> extensions MAY impose extra conditions which require other named
>>> graphs to be interpreted in particular ways. </p>
>>>
>>> Pat
>>
>> Something needs to be said that structural bnode-isomorphism and the
>> meaning of the dataset are now separate issues, unlike graphs.
>>
>> # Dataset D1 - links to bnode graph
>> { :s1 :observed _:a }
>> _:a {:s2 :p2 456 }
>> _:b {:s2 :p2 123 }
>>
>> # Dataset D2 - same meaning as D1, no such link
>> { :s1 :observed _:z }
>> _:a {:s2 :p2 456 }
>> _:b {:s2 :p2 123 }
>>
>> # Dataset D3
>> { :s1 :p _:z }
>> <g> {:s2 :p _:z }
>>
>> # Dataset D4 - same meaning as D3, bnode not now shared
>> { :s1 :p _:a }
>> <g> {:s2 :p _:z }
>
> I think that's what ISSUE-136 is all about, isn't it?
>
>    http://www.w3.org/2011/rdf-wg/track/issues/136

It's orthogonal; this does not depend on labelling semantics.  Just 
assume it's the same in D1/D2, and D3/D4 as might happen if a system 
received such a trig file and republishes it.  Add triples if you want 
to mark the kind of labelling, the example still applies.

The datasets have different structures; the linking has changed just by 
replacing one default graph by another simply-entailed one.  This needs 
to be pointed out close to any text about dataset meaning.

[[ 5.3 Simple Entailment
Entailment refers only to the truth of RDF graphs, not to their 
suitability for any other purpose.  It is possible for an RDF graph to 
be fitted for a given purpose and yet validly entail another graph which 
is not appropriate for the same purpose.
]]
although that then is about subgraphs.


As blank nodes are said to facilitate denotation, let's stick to that 
for the discussion here.

----- s1 observes something.
----- The something is graph value {:s2 :p2 456 }
{ <> a rdf:BoundDataset .
   :s1 :observed _:a .
}
_:a {:s2 :p2 456 }


----- s1 observes something
----- There is a graph value floating around. Not connected
{ <> a rdf:BoundDataset .
   :s1 :observed _:z .
}
_:a {:s2 :p2 456 }

which are different.

	Andy

>
>
>
> --
> Markus Lanthaler
> @markuslanthaler
>
>

Received on Thursday, 20 June 2013 16:09:34 UTC