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Re: complete vs partial graph semantics

From: Sandro Hawke <sandro@w3.org>
Date: Tue, 24 Apr 2012 22:51:44 -0400
To: David Wood <david@3roundstones.com>
Cc: Pat Hayes <phayes@ihmc.us>, Andy Seaborne <andy.seaborne@epimorphics.com>, public-rdf-wg@w3.org
Message-ID: <1335322304.9663.145.camel@waldron>
On Tue, 2012-04-24 at 09:22 -0400, David Wood wrote:
> Hi all,
> 
> On Apr 12, 2012, at 14:06, 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. 
> > 
> 
> 
> It seems to me that the motivation of partial semantics could be made
> by making a concrete example:
> 
> 
> Trig Document 1 (D1):
>    <u> { <#sandro> <foaf:knows> <#ivan> }
> 
> 
> Trig Document 2 (D2):
>    <u> { <#sandro> <foaf:knows> <#andy> }
> 
> 
> So, using Pat's contexts (*without* using the term "graph" for
> anything, because it is still confusing), the union of the graphs
> makes sense to me:
> 
> 
> <u> { <#sandro> <foaf:knows> <#ivan>, <#andy>) }
> 
> 
> That's similar to what Andy wrote in [1], but maybe a bit stronger to
> make the point.
> 
> 
> Now, one SHOULD NOT (in RFC 2119 sense) do that with:
> 
> 
> <u> { <#measurement> <ex:equals> "7" }
> and
> <u> { <#measurement> <ex:equals> "4" }
> 
> 
> ...but the ability to be mistaken and lie like that is just the
> flexibility that we want in RDF.  Any greater attempt to enforce a
> version of the truth risks shackling the user community in ways that
> will both violate our use cases and restrict adoption.

I think your example kind of muddies the water, more than it clears
things up, because it involves the meaning of the terms inside the curly
braces.  But the curly braces are opaque in 6.1, so the terms inside
don't matter that way.

Perhaps the simplest framing is this.

If you and I both accept this is true:

   <u> { <a> <b> <c> }          # D1

is it then possible that this could also be true:

   <u> { <a> <b> <d> }          # D2

?   And if it is, does that mean <u> is now associated with two
different graphs?  Or with one bigger graph?  Or with all three?

For a long time, it seemed to me D1 and D2 could not both be true, but
now I see some sense to the idea of "all three".  It makes sense of just
think of <u> as tagging the triples in the graph, making quads.

    -- Sandro
Received on Wednesday, 25 April 2012 02:51:54 UTC

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