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RE: DTTF: another summary

From: Smith, Michael K <michael.smith@eds.com>
Date: Tue, 7 May 2002 06:17:51 -0500
Message-ID: <B8E84F4D9F65D411803500508BE322140D9C2DA9@USPLM207>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>, www-webont-wg@w3.org
Sorry I'm slow to reply.  Was out of town last week.

Jeremy stated:

> A monotonic layering would be one in which
> 
> if
>   a rdfs-entails b
> then
>   a owl-entails b
> 
> and both rdfs-entails and owl-entails are monotonic.
> This is Mike's SEMANTIC PROPERTY 1.

I don't think of this as SEMANTIC PROPERTY 1, since the whole point of
properties 1-4 was to discuss T and TINV and their impact on semantics.

> I drop Mike's T and TINV by noting that we have agreed
> that the syntax for OWL is RDF graphs which is also the
> syntax for RDFS.

The log of the F2F notes that 

  o  that there is a presentation syntax and an underlying syntax and a
transform 
  o  some form of presentation syntax is requirement 
  o  RDF is underlying syntax 

I guess I am not clear on what was meant by the last item.  (My excuse
is that I was not able to attend the F2F.) I took that to mean that we
could translate OWL syntax to RDF syntax.  I did not take it to mean
that it is a requirement that all RDF be stateable in OWL (which is a
corollary to Jeremy's monotonic layering above).  This assumption had
a variety of reasons, including the semantic issues that Peter and Pat
have presented, weird RDF lists, and some messages that talked about
translating OWL to RDF.

So, what did the resolution at the F2F mean?  In particular:  

1. Did it mean that it is a requirement that all RDF statements are
statements in OWL?  And therefore have to be given an interpretation in
OWL?  I'm having trouble reading that into the resolution, but perhaps
it was part of the discussion.  If so, yikes.

2. Did it mean that RDF must be the 'abstract' syntax that the OWL formal
semantics embraces?  

Surely not.  I am pretty sure that whoever formalizes the semantics
does not want to have to define part of it in terms of
Subject-Predicate-Object RDF structures, which (in the absence of
RDF:DARK) would seem to be a requirement if all OWL is to be
expressible in RDF. 

If RDF is not the selected abstract syntax for OWL, then T and TINV are
worth discussing.  Per

http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0200.html

- Mike

Michael K. Smith
EDS Austin Innovation Centre
98 San Jacinto, #500
Austin, TX 78701
512 404-6683

> -----Original Message-----
> From: Jeremy Carroll [mailto:jjc@hplb.hpl.hp.com]
> Sent: Friday, May 03, 2002 4:46 AM
> To: www-webont-wg@w3.org
> Subject: DTTF: another summary
> 
> 
> 
> It seems symptomatic of being difficult to refuse to even 
> agree on where we
> are at ...
> 
> I am difficult.
> 
> 
> I believe we have three live proposals:
> 
> - comprehensive entailments: Jeremy
>   [1]
> - dark owl: Peter
>   [2], [3]
> - dark lists: Pat
>   [4]
> 
> We are agreed that the first does not use dark triples
> and that the second and third do.
> 
> Pat and Peter have asserted that comprehensive entailments
> involves significantly more risk and research than the
> other two proposals. I have not conceded this.
> 
> I believe that DanC has understood my proposal.
> 
> There has been no evidence that anyone has understood either
> of the other proposals. I have claimed to have understood
> both, but seem to have been mistaken vis-a-vis Pat's.
> I have also proved unable to articulate Peter's.
> 
> In particular there does not appear
> to be any evidence that Pat and Peter agree on anything other
> than that the right proposal involves dark triples. Since the
> "right proposal" is an unbound variable in that agreement it
> seems to me to be high risk to build on that agreement.
> 
> 
> In my view, we have three distinct issues:
> 
>   comprehension
>   paradox
>   layering
> 
> 
>   comprehension
>   =============
> 
> How does the semantics of OWL account for the entailment
> 
> _:x <rdf:type> <student> .
> _:x <rdf:type> <employee> .
> 
> entails
> 
> _:x <rdf:type> _:inter .
> _:inter <rdf:type> <owl:class> .
> _:inter <owl:intersectionOf> _:list .
> _:list <rdf:type> <owl:List> .
> _:list <owl:first> <student> .
> _:list <owl:rest> _:tail .
> _:tail <rdf:type> <owl:List> .
> _:tail <owl:first> <employee> .
> _:tail <owl:rest> <owl:nil> .
> 
> 
> (Perhaps we don't really need _:x here at all).
> 
>   paradox
>   =======
> 
> How are paradoxes like the Patel-Schneider paradox avoided.
> 
>   layering
>   ========
> 
> What is the relationship between RDF entailment,
> RDFS entailment and OWL entailment.
> 
> This is explored by Mike Smith [5].
> There is a particularly pertinent form if the lower
> layers of OWL reuse the terms from rdfs.
> 
> For a document that uses rdf and rdfs vocabulary and
> no OWL vocabulary is OWL entailment monotonically
> layered on top of RDFS entailment.
> 
> 
> ******************************
> 
> On the relationship between the proposals and the problems.
> 
> Comprehension + Paradox
> =======================
> 
> The comprehension rules are shared between the
> comprehensive entailments and the dark lists proposal [6].
> 
> These rules are the way both these proposals
> address the comprehension issue without falling into
> the paradox problem.
> 
> In particular, my attempt to articulate to Pat how
> I understood Peter's proposal as addressing Peter's
> paradox [7] fizzled out.
> 
> I don't feel we have seen from Peter an account of how
> either issue is addressed.
> 
> 
> Layering
> ========
> 
> Peter and Mike see the impossibility of layering as
> self-evident.
> 
> I have disputed this, seeing an ill-formed list as a semantic
> rather than a syntactic problem.
> 
> I believe that a clean monotonic layering of OWL on top of RDFS
> is highly desirable, and that we need to have good evidence of
> its impossibility before not attempting it.
> 
> A monotonic layering would be one in which
> 
> if
> 
>   a rdfs-entails b
> 
> then
> 
>   a owl-entails b
> 
> and both rdfs-entails and owl-entails are monotonic.
> This is Mike's SEMANTIC PROPERTY 1.
> I drop Mike's T and TINV by noting that we have agreed
> that the syntax for OWL is RDF graphs which is also the
> syntax for RDFS.
> 
> My belief that this is an important goal is based on the
> following assumptions
> - the semantic web project is fairly high risk
> - the key risks are in terms of semantics and scale
> - monotonicity is a key distinctive feature of the
>   semantic web that addresses these risks
>   and makes it a plausible bet
>   (one that I am prepared to spend a chunk of my
>   life on).
> 
> I wonder whether Pat and Peter see strict layering as
> advocating that the object denoted by a URI in the RDFS layer
> is the same as that in the OWL layer. I see that as an
> irrelevance. Layering expressed using Mike semantic property
> 1 does not reuse an RDFS interpretation as an OWL interpretation.
> 
> I note that this monotonic layering is less important
> than the monotonicity of the individual layers, and I
> am certainly open to Pat's fig-leaf position, given
> a reasoned argument as to why some aspect of a monotonic
> layering either won't work or has excessive cost on some
> other dimension.
> 
> No one has yet put such an argument.
> 
> My proposal does respect this constraint.
> 
> 
> *****************************
> 
> An important aspect of the difference between the
> proposals is syntax vs semantics.
> 
> The dark stuff is seen as syntactic, the not dark stuff
> is seen as semantic. Hence whenever we are talking about X
> there is often miscommunication because the advocates of
> dark X think we are discussing the syntax and its semantics,
> whereas the opponenets assume we are talking at only a semantic
> level. Quite who is on which side varies with X.
> 
> 
> 
> References:
> 
> [1] Jeremy: Comprehensive Entailments
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0155.html
> 
> [2] Peter: one *quick* proposal
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0229.html
> 
> 
> [3] Peter: longer proposal
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0241.html
> 
> [4] Pat: proposal
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0254.html
> 
> [5] Mike: layering
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0200.html
> 
> [6] Pat (in reply to Jeremy): comprehension
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0338.html
> [[[ [Pat]
> In RDF it doesnt. In OWL it would come from an OWL semantic
> constraint of the form that if JOhn is in A and JOhn is in B then
> JOhn is in (A intersect B).
> ]]]
> 
> [7] Jeremy & Pat: Peter & paradox
> http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0343.html
> 
> [[[
> [ jeremy on Peter's approach ]
> > >>  >Potential paradoxes, like the Patel-Schneider paradox (Test
> > Case C) are
> > >>  >resolved outside of DAML+OIL.
> > >Pat:
> > >>  'Outside' means what?
> > >
> > >
> [ jeremy again ]
> > >In the model, because of set theoretic constraints on the model.
> > >But an axiomatisation of the DAML+OIL model theory
> >
> [ pat ]
> > Please don't use meaningless phrases.
> [ jeremy ]
> I am sorry, I clearly didn't use the right language.
> I will not try and indicate how darkening all of owl solves the
> Patel-Scheider paradox, suffice to say I think it does. Peter 
> can give a
> fuller account if he wants.
> ]]]
> 
> 
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Received on Tuesday, 7 May 2002 07:18:07 GMT

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