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Re: "Tagged Graphs" (was Re: complete vs partial graph semantics)

From: Ivan Herman <ivan@w3.org>
Date: Fri, 13 Apr 2012 09:22:55 +0200
Cc: Pat Hayes <phayes@ihmc.us>, public-rdf-wg@w3.org
Message-Id: <15D5C25D-36C7-45A8-82C1-42375CE3F94C@w3.org>
To: Sandro Hawke <sandro@w3.org>

isn't it the point where the question I was asking about the role of rdf:Graph may come in?

Ie: if

<u> { ... } .
<u> a rdf:Graph .

then what we say is that <u> really denotes the graph, and I can very well say that the (maxCard 1) feature does make sense. However, if <u> is not of that type, then it is a 'label' (or a 'tag'), meaning that the partial graph behavior does make sense because, as Pat said, it reflects a different intuition.

I think that the current attempt for semantics may actually reflect that well; although it would also be possible to modify Condition #1 in [1] to hold only if the two ui-s are of type rdf:Graph.


[1] http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1/Sem

On Apr 12, 2012, at 23:41 , Sandro Hawke wrote:

> On Thu, 2012-04-12 at 11:06 -0700, Pat Hayes wrote:
>> On Apr 12, 2012, at 8:09 AM, Sandro Hawke wrote:
>>> I'm having a lot of trouble understanding the motivation for
>>> partial-graph semantics.   It seems to me like a kind-of-cool but
>> way-too-complicated idea.
>> OK, let me motivate it by providing a different intuition. You have been consistently thinking of the graph label as being an actual name for the graph (the one it is next to in the TriG document, that is), or at any rate for some graph or other which is closely related to the graph. That is, the graph name denotes a graph.  But going back to the intuitions built into Antoine's semantics, it is more natural there to think of the label as identifying not the graph itself, but a context within which to interpret the graph; and then, it is both natural and semantically valid to infer the merge of two graphs with the same label. 
>> I think that this may be a fundamental split between two intuitions about what the graph "name" really names, and that this split may be irreconcileable; and the test case is
>> <u> { <a> <b> <c> }
>> <u> { <d> <e> <f> }
>> are consistent and together entail ??
>> <u> ( <a> <b> <c>
>>           <d> <e> <f> }
>> A: No when <u> names the graph, yes when it names some kind of larger interpretation context. 
> So, in that case, it's more like a label or tag on a triple, right?  We
> can put whatever labels we want on whatever triples we want, and then
> later ask about which triples happened to have a particular label....
> Here, the trig document:
>    <u> { <a> <b> <c> }
> might be read as: the triple <a> <b> <c> is tagged with the object I(u).
> Then the SPARQL query expression "GRAPH <u> { ?s ?p ?o}" would be
> understood as asking about all the triples which, as far as that
> endpoint knows, currently are tagged with the object named <u>.
> Okay, this seems like a coherent system, sure.   Does it work for the
> use cases?     How about cc:license....
> How do I write a trig file in which I publish two collections of
> triples, one of which I license cc:by and the other cc:by-nc ?
> I'd think something like:
>   { <g1> cc:license cc:by, a rdf:Graph.
>     <g2> cc:license cc:by-nc, a rdf:Graph.
>   }
>   <g1> { ... these triples can by copied just giving attribution ... }
>   <g2> { ... these triples need attribution and non-commercial use ... }
> (I'm not sure we need the rdf:Graph in there, with this approach.)
> Isn't this too fuzzy / open-ended?    What if someone else uses <g1> to
> mean something else?   Or, how could I pick <g1> so that I'm right and
> their wrong, if they use it for something else?
> Given this imprecision, can I just do this:
>   cc:by { ... these triples can by copied just giving attribution ... }
>   cc:by-nc { ... these triples need attribution and non-commercial use ... }
> I dunno.   Maybe this works.   It sure is simpler.
>   -- Sandro

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Friday, 13 April 2012 07:21:14 UTC

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