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Re: Bags (was: closing semantic issues)

From: Dan Connolly <connolly@w3.org>
Date: Thu, 08 Nov 2001 12:51:17 -0600
Message-ID: <3BEAD425.60108@w3.org>
To: Pat Hayes <phayes@ai.uwf.edu>
CC: Graham Klyne <Graham.Klyne@MIMEsweeper.com>, w3c-rdfcore-wg@w3.org
Pat Hayes wrote:

>> At 05:35 PM 11/6/01 -0600, Pat Hayes wrote:

>> if we then learn that _:b1 and _:b2 are equivalent,
> ....but wait. Do we want to consider reasoning with equivalences at all? 

We certainly don't want to preclude it; the DAML+OIL stuff wouldn't
layer on top, otherwise, would it?

> That gets us into a whole lot of tar-pits which we might want to just 
> try to avoid, maybe (please?)


> So heres the rule. If we have a triple
> foo rdf:type rdf:Bag
> in a graph, then say that the nodes which are in the object position of 
> a triple of the form
> foo rdf:_n <object>
> in that graph are the 'foo member nodes'.

No; you can't conclude from no information that there are no others.

And I do think that each of the _:n properties is functional;
	_:x rdf:_1 "abc".
	_:x rdf:_1 "def".
is a contradiction (is that in the model theory? subject/predicate/object
are also functional).

So the best I can think of is that if we have

  _:b rdf:type rdf:Bag.

then there's some _:bc where

  _:b rdfs:bagContents _:bc.

and where any X with

  _:b rdf:_NNN X.

we have

  X rdf:type _:bc.

(hmm... that might end up with a literal subject. That
doesn't bother me, but if it bothers other folks,
I suppose some analog of ICEXT, say IBAG is in order.
Ug... this the second really serious design bug
I've seen with RDF containers).

> Then any graph gotten by 
> permuting the arcs to the foo member nodes, and replacing  the node foo 
> by a new bnode, should be entailed by the first graph.
> Tell you want, lets agree not to talk about rdf:Bag-closures, OK?

I'm not sure what a bag-closure is, but if it's the same issue as


then I don't agree not to talk about it ;-)

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 8 November 2001 13:51:21 UTC

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