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Re: Labelled graphs

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 24 Apr 2012 16:05:41 +0100
Message-ID: <4F96C145.8030203@epimorphics.com>
To: public-rdf-wg@w3.org


On 24/04/12 13:04, Sandro Hawke wrote:
> (mostly agreement, a few details)
>
> On Tue, 2012-04-24 at 12:03 +0100, Andy Seaborne wrote:
>>
>> On 17/04/12 16:59, Guus Schreiber wrote:
>> ...
>>
>>> An attempt at formulating a possible conclusion/consensus from this thread:
>>>
>>> * Non-typed labels are simply associations, no special semantics
>
> There are some semantics, though: the label IRI (or blank node) denotes
> something (maybe call it a "labeling object"), and that something is
> associated with the graph.

Given the "something" indirection, whether that counts as "semantics" or 
not is a bit moot to me.  It's "no fixed semantics".

The absolute minimum is to be able to ship a trig file, so 
syntax+labels.  Given this very low level building block, treating 
datasets as just a packing format, and it's graphs that carry semantics. 
  From there, the rest can be built on top because it's based on adding 
triples.

> This differs from SPARQL Datasets, where
> the label IRI is directly associated with the graph.

To quote SPARQL 1.0:
"""
the relationship between an IRI and a graph in an RDF dataset
is indirect.
"""

> The difference doesn't show up in normal SPARQL, but would be visible if
> there was reasoning, such as with owl:sameAs.   See these test cases:
> http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1#Graph_Labels
>
>>> * Typed labels: we do not seem to come up with more than these two:
>>>
>>> 1. The label is typed as a rdf:StaticGraphContainer:
>>> the graph labeled is a g-snap of the label URL
>
> I'm not convinced we can make this kind of definition work right, but
> I'm not opposed to trying.  It will have to bring TAG language into the
> RDF specs for the first time.   I'm also not sure we need "Static",
> since the RDF view is still that the universe is static.

And that's part of the whole issue :-)

	Andy

>
>>> 2. The label is types as a rdf:Graph:
>>> the label denotes the graph it labels
>
> Yes.
>
>>> * When the same label is used multiple times in the same dataset, the
>>> graph is
>>> assumed to be the union of the graphs labeled with it
>
> This is the "partial-graph semantics" view, which I can live with, but
> some people have expressed opposition.  We should probably try some
> straw polling on it.
>
>>> The appears to be in line to the 6.1 design, with some
>>> modifications/specializations.
>
> I wonder if we can't adopt something close to 6.1, close pretty much all
> the open GRAPHS issues, then open a few new ones, like
> partial-vs-complete-graph semantics and whether/how to define
> GraphContainer.
>
>      -- Sandro
>
>>> Guus
>>
>> (sorry for the delay - was not at work)
>>
>> Guus - nice summary.
>>
>> 	Andy
>>
>>
>>
>
>
>
Received on Tuesday, 24 April 2012 15:06:19 UTC

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