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[Fwd: [Moderator Action] RE: RDF Semantics: Interpretations and Modelling]

From: Eric Miller <em@w3.org>
Date: 04 Feb 2003 09:31:10 -0500
To: w3c-rdfcore-wg@w3.org
Message-Id: <1044369071.5935.17.camel@cherry>

-----Forwarded Message-----

From: Ossi Nykänen <onykane@butler.cc.tut.fi>
To: pat hayes <phayes@ai.uwf.edu>
Cc: Massimo Marchiori <massimo@w3.org>, w3c-rdfcore-wg@w3.org
Subject: [Moderator Action] RE: RDF Semantics: Interpretations and Modelling
Date: 04 Feb 2003 04:40:18 -0500



Dear Patrick Hayes,

Thank you for the clarification.

> > This seems
> > to nullify the work and efforts spend on defining,
> > e.g., the rdf:bag container
>
> What work and effort? What definition?

This is my opinion only but if RDF Semantics (note: as a design choice) is
not willing to differentiate, e.g., bags and alts in entailments, then
perhaps the model-theoretic approach isn't suitable for the purpose.

My comment is purely practical. If differentiating bags and alts is
considered important in RDF, this makes you wonder the role of RDF
Semantics in applications of RDF (*). In practice, it would seem to be
safer to use, e.g., (now imaginary) ibm-glossary:Bag and ibm-glossay:Alt
with (perhaps rather restricting but) fixed entailment semantics  given by
IBM than rdf:Bag and rdf:Alt, if each time people used, e.g., rdf:Alt they
would have to (in addition) state (somehow): "My interpretation is that
rdf:Alt does not entail all its members but rdf:Bag does!"

(*) This is the work and effort and definition: the work of coming up the
concept rdf:Bag and saying that it is different from rdf:Alt. My opinion
is that semantics should say exactly how they are or could be different,
at least in an informative subsection (when, e.g., associated with a foo
predicate). If not, people make their own bags and alts and the W3C name
for the concepts is informative only (perhaps it should be?).

Very best regards,

--Ossi



Ossi Nykänen                              Tel   +358 3 3115 3544
Tampere University of Technology          Fax   +358 3 3115 3549
DMI / W3C Finnish Office                  Email ossi@w3.org
P.O.Box 553, FIN-33101 Tampere, Finland   Web   www.w3c.tut.fi


On Mon, 3 Feb 2003, pat hayes wrote:

> >  > #1.) RDF semantics does not define interpretation for containers or
> >>  collections (etc.). Since RDF semantics treats URIs as parameters, this
> >>  means that RDF models containers can interpreted arbitrarily.
>
> That is too strong. There is a clearly defined intended meaning for
> the rdf:Bag concept: it says that the container in question is a bag,
> and the container membership properties tell you what its members
> are.  The order in which they tell you this is irrelevant, since the
> thing is a bag. The key point however is that this information -
> about being a bag - does not impose any restrictions on formal
> interpretations which can be expressed as valid entailments. There
> are no valid entailments about rdf Bags that are not also valid of
> rdf Seqs; the rdf model theory isn't able to distinguish between bags
> and sequences; other, of course, than simply by asserting that some
> of them are called 'bags' and some are called 'sequences'. And this
> is not surprising, because this distinction only makes sense in a
> semantics which has a notion of state, so that it makes sense to talk
> about what happens if you RE-order the elements. RDF semantics is
> state-free. So this isn't a bug in the spec, or an omission; it is a
> reflection of a very fundamental semantic property of assertional
> languages, of which RDF is one.
>
> >This seems
> >>  to nullify the work and efforts spend on defining, e.g., the rdf:bag
> >>  container
>
> What work and effort? What definition?
>
> >or rdfs:comment. (From the viewpoint of entailments, why bother
> >>  using bag if it's "just" a URIref.)
> >
> >Ossi, this is the Bag/Alt issue, raised in May 2002:
> >http://lists.w3.org/Archives/Public/www-rdf-comments/2002AprJun/0112.html
> >AFAIK never replied yet.
> >Incidentally, the same wrong argument pointed therein appears again
> >in the current last call draft.
>
> Im not sure which 'wrong argument' you are referring to. I stand by
> everything I said that is  included in the above-referenced message.
> In particular,
>
> " If
> _:xxx [rdf:type] [rdf:Bag] .
> >  _:xxx [rdf:_1] <ex:a> .
> >  _:xxx [rdf:_2] <ex:b> .
> >
> >  entails
> >
> >  _:xxx [rdf:_1] <ex:b> .
> >  _:xxx [rdf:_2] <ex:a> .
> >
> >  then it also must entail
> >
> >  _:xxx [rdf:type] [rdf:Bag] .
> >  _:xxx [rdf:_1] <ex:a> .
> >  _:xxx [rdf:_2] <ex:b> .
> >  _:xxx [rdf:_1] <ex:b> .
> >  _:xxx [rdf:_2] <ex:a> .
> >
> >  and by suitable reordering, it will entail that ALL members of the
> >  bag are in ALL positions."
>
> is a correct argument, and your response to it is incorrect.
>
> Pat
>
>
>
> --
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-- 
eric miller                              http://www.w3.org/people/em/
semantic web activity lead               http://www.w3.org/2001/sw/
w3c world wide web consortium            http://www.w3.org/
Received on Tuesday, 4 February 2003 09:33:42 EST

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