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Re: Labelled graphs

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 25 Apr 2012 08:46:06 -0400
To: Andy Seaborne <andy.seaborne@epimorphics.com>
Cc: Ivan Herman <ivan@w3.org>, public-rdf-wg@w3.org
Message-ID: <1335357966.9663.274.camel@waldron>
On Wed, 2012-04-25 at 13:11 +0100, Andy Seaborne wrote:
> 
> On 25/04/12 12:28, Ivan Herman wrote:
> >
> > On Apr 25, 2012, at 05:16 , Sandro Hawke wrote:
> >
> >> On Tue, 2012-04-24 at 16:05 +0100, Andy Seaborne wrote:
> >>>
> >>> 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".
> >>
> >> Here's the part that's important to me:
> >>
> >>         Under OWL entailment and our dataset semantics, does
> >>            {<u1>  owl:sameAs<u2>  }
> >>            <u1>  {<a>  <b>  <c>  }
> >>         entail
> >>            <u2>  {<a>  <b>  <c>  }
> >>         ?
> >>
> >
> > FWIW, in the case of http://www.w3.org/2011/rdf-wg/wiki/Graphs_Design_6.1/Sem the answer is clearly yes.
> 
> I think this is at a different level.
> 
> (I think that) the most basic thing we (this WG) needs to do is define 
> syntax so that things do not go wrong.  This does not need to fix the 
> semantics for all time.

To be clear, are you saying you would like the entirety of this WG's
output concerning "named graphs" to be a Recommendation for the grammar
of TriG?

That might be worth a straw poll in today's meeting.

I note that our charter says:
        
        Required features
              * Standardize a model and semantics for multiple graphs
                and graphs stores 
                
... but, of course, the charter can't actually make us do something if
we don't want to.  It also says we'll be at Last Call in May 2012.  So,
if we give the deadline priority, then yes, we probably have to give up
on producing a semantics for Named Graphs.

> We have some interesting approaches on top of that (6.1, RDFC etc) 
> emerging, and we have identified different use cases 
> (rdf:StaticGraphContainer, rdf:Graph).  Prov-WG and eGov-WG may also 
> have something to say.
> 
> The approaches look interesting but they have not been "field tested". 
> If the syntax and collision avoidance is set up right, this WG has 
> enabled the further refinements over time beyond the WG timescale.
> 
> As to owl:sameAs:
> 
> 1/ owl:sameAs works well on properties and classes, less well on 
> individuals (is your "London" the same as my "London" mine?  For all time?)

This is somewhat off-topic, but I don't agree.  To me, owl:sameAs is
basically another way of using the same IRI to identify something.

Do we both mean the same thing by dbpedia:London ?   If we do, then we
can either use that IRI, or we can use our own IRIs and say they are
owl:sameAs that IRI.   The flexibility to do it either way is quite
useful for managing other aspects of the system.

> 2/ Actually as written, the answer to Sandros example is
> 
> "yes, same dataset" (iri denotes X, X associated with graph + owlSameAs 
> then the <u1> <u2> denote the same X because the assertion in a graph so 
> uniform denotation applies).
> 
> "no, across datasets" (all bets are off, without further knoweledge 
> because two uses of the same <u> may be, say, different views of the 
> same StaticGraphContainer. i.e. <u> and <u> labelling may be different, 
> different people observed the web at different times.  That's reality. 
> Time enters the picture.

This sounds to me like the whole context issue, which I think we can and
should keep separate.   I mean to be asking my entailment question
exactly the same as all the entailment questions in the RDF and OWL test
suites.   This is all taking place in the same context - the same time,
the same place, the same observer, if you like.

For example there's a test (datatypes/test008) like:
      <a> <b> 10.
      <c> <d> 10.
entails
      <a> <b> _:x.
      <c> <d> _:x.

Obviously, this is assuming the 'b' property of 'a' hasn't changed,
etc.   

    -- Sandro
Received on Wednesday, 25 April 2012 12:46:23 UTC

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