W3C home > Mailing lists > Public > public-rdf-wg@w3.org > December 2011

Re: dataset semantics

From: Sandro Hawke <sandro@w3.org>
Date: Sun, 18 Dec 2011 23:58:00 -0500
To: Pat Hayes <phayes@ihmc.us>
Cc: William Waites <wwaites@tardis.ed.ac.uk>, david@3roundstones.com, public-rdf-wg@w3.org
Message-ID: <1324270680.6252.1488.camel@waldron>
On Sat, 2011-12-17 at 10:02 -0600, Pat Hayes wrote:
> On Dec 17, 2011, at 7:09 AM, Sandro Hawke wrote:
> 
> > On Sat, 2011-12-17 at 10:29 +0000, William Waites wrote:
> >> On Sat, 17 Dec 2011 00:43:38 -0500, Sandro Hawke <sandro@w3.org> said:
> >> 
> >>    sandro> We haven't quite figured that out yet.  I'm proposing one
> >>    sandro> part of that is that a dataset being true implies its
> >>    sandro> default graph is true.
> 
> > In terms of an entailment test:
> > 
> >    <a>  { <b> <c> <d> }
> > 
> > does NOT entail
> > 
> >   { <b> <c> <d> }
> > 
> 
> 
> Really?? Is this generally accepted, or is it your own conclusion?

This is just my strawman proposal, to try to get us moving along.

>  Because this has the (to me surprising) consequence that publishing a dataset does not assert ANY of the named graphs in it. Which leaves me wondering what the point of having datasets can possibly be in the first place. Does the Semantic Web consist mostly of unasserted fiction? 

Well, my earlier entailment test was about how the default graph *is*
asserted.  But, right, I'm suggesting that the others are not
automatically asserted.

Your surprise here makes me think there are two *very* different kinds
of use cases for transmitted datasets.

1.  Someone wants to publish some triples, but they want to annotate
various subgraphs among the triples.  I think that's the case you're
thinking of.  So all the triples are asserted, but also, they can say
things about subgraphs.

2.  Someone wants to say things about graphs/subgraphs that other people
have asserted, without necessarily buying into them.  That's the case I
was thinking of, where people can talk about, say, statements made in
the past, or statements of unknown veracity.   It wouldn't work for them
to have to assert those graphs just to say they are no longer true.

So, how can we support both kinds?

- we could have some kind of flag outside the document, like a different
media-type for each semantics

- we could have some kind of global flag inside the document, like a
triple like { <> a rdf:Type_A_Dataset }

- we could have some kind of flag on each labeled subgraph, saying
whether it is also asserted; maybe a keyword, like INCLUDED or
EXCLUDED.

- in the default graph, we could explicitly assert some of the subgraphs
(which would require being somehow able to refer to them).

At this point, the second of these strikes me as the least painful, with
possibly the third overriding it, on a per-subgraph basis.

BTW, I keep saying "subgraph", because several people have said they
need bnodes to be shared between these things, and as I understand the
RDF semantics, that means they shouldn't be considered graphs in their
own right, just subgraphs of some larger (not-necessarily-asserted)
graph.

    -- Sandro
Received on Monday, 19 December 2011 04:58:11 GMT

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