W3C home > Mailing lists > Public > public-rdf-wg@w3.org > December 2013

Re: New editor's draft of RDF Datatset Semantics

From: Andy Seaborne <andy@apache.org>
Date: Fri, 13 Dec 2013 16:37:51 +0000
Message-ID: <52AB37DF.5080204@apache.org>
To: public-rdf-wg@w3.org
On 13/12/13 15:49, Antoine Zimmermann wrote:
> Le 13/12/2013 13:35, Andy Seaborne a écrit :
>> On 12/12/13 21:08, Antoine Zimmermann wrote:
>>> The new draft addresses most of Pat's comments. I added 2 issues to it.
>>> I also added a section that reflects Sandro's box dataset semantics,
>>> following Guus' suggestion, and also made some changes in response to
>>> Peter initial comments.
>>>
>>>
>>> https://dvcs.w3.org/hg/rdf/raw-file/default/rdf-dataset/index.html
>>>
>>>
>>> If it looks ok, we can vote by email to make it a FPWD. Sorry for not
>>> having done this before yesterday teleconf.
>>
>>
>> [[
>> 3.2 Default graph as union or as merge
>>
>> It is sometimes assumed that named graphs are simply a convenient way of
>> sorting the triples but all the triples participate in a united
>> knowledge base that takes the place of the default graph. More
>> precisely, a dataset is considered to be true if all the triples in all
>> the graphs, named or default, are true together.
>> ]]
>>
>> This starts talking of dftGraph = union of named graphs, not a super
>> set, but then says it is all the triples in graphs, named or default.
>>
>> Shouldn't the default graph be exactly the union (version 2: merge) of
>> the named graphs?
>
> The semantics defines the truth of all datasets. Not only the datasets
> with a default graph equal to the union of the named graphs.
>
>
>> Or there needs to be some rewording because "default graph" is being
>> used is different ways.
>
> In different ways? What way is different from what other way?

In one case, there is no ground data in the dft graph, in the other 
there is.

>
>
>> [[
>> This description allows two formalizations of dataset semantics,
>> depending on how blank nodes spanning several named graphs are treated.
>> ]]
>>
>> It is worth nothing that TriG and N-quads use document-scoped blank node
>> labels.
>
> worth nothing? or worth noting?

"noting"

> In any case, the formal semantics is
> agnostic wrt the serialisation syntax used. The definition of RDF
> datasets allows for shared blank nodes across several named graphs, and
> the semantics has to apply to all RDF datasets.
>
>> I don't know of any system that does NGs+dftgraph -> dftGraph of
>> dataset.  Are there any?
>
> Sesame and OWLIM apply reasoning on the union of all named graphs to
> generate triples that are then inserted into the default graph. This
> materialisation of inferences creates a dataset where the default graph
> is a strict superset of the union of named graphs.

But that's not what the example is - as you describe it, only triples 
that in NGs or inferred are in the inferred/materialisation dft graph. 
Any in the original dft graph are lost.

>
>
>> 3.6 Quad semantics
>>
>> Worth mentioning about the empty graph.
>
> Ok, empty named graphs cannot be represented as quads, but this is
> essentially a syntactic issue. Still, I'd say it could be noted
> nonetheless.
>
>
> AZ.
>
>>
>>      Andy
>>
>>
>>
>
Received on Friday, 13 December 2013 16:38:21 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 17:04:37 UTC