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Re: LANG: Nested Class definitions and the RDF striped syntax

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 22 Mar 2002 12:48:57 -0500
To: jonathan@openhealth.org
Cc: Frank.van.Harmelen@cs.vu.nl, www-webont-wg@w3.org
Message-Id: <20020322124857L.pfps@research.bell-labs.com>
From: "Jonathan Borden" <jonathan@openhealth.org>
Subject: Re: LANG: Nested Class definitions and the RDF striped syntax
Date: Fri, 22 Mar 2002 23:31:23 -0500

> Peter F. Patel-Schneider wrote:
> 
> >
> > This is not sufficient to prevent round-tripping problems.
> >
> > What would be sufficient would be to also show that there is an inverse
> > transform from the ``top-level'' syntax to the ``nested'' syntax that
> > results in a knowledge base close to the original.  Otherwise it is
> > possible that a nested syntax knowledge base is transformed into a
> > different-looking knowledge base, and that the differences in appearance
> > are significant.
> 
> 1) You are suggesting that OWL-Lite will solve the round tripping problem

Actually, I don't believe that OWL-Lite will solve the round-tripping
problem.  I believe that the round-tripping problem is inherent in RDF,
unless the encoding into RDF looks very different than DAML+OIL.

> 2) I agree, and suggest that OWL with nested class definitions can be
> transformed into 'top level'

I believe that this is not an adequate solution.

> 3) I am not sure that any _requirement_ for the language states that one
> must be able to roundtrip between the lexical (XML) syntax and RDF

I do not know if there is a specific portion of the requirements document
that relates to this.  However, it is tied up with the ease of use
requirement.

> 4) XML document editors have difficulty 'roundtripping' between XML
> documents and the internal DOM format (for example), these difficulties are
> well known, well described, editors need to deal with it.
> 5) However, I am suggesting that tools which wish to roundtrip create
> ontologies using the 'top level' idiom, in which case such tools and their
> users will be happy.

I do not believe that this is an adequate solution, for the reasons stated
in 

Sean Bechhofer, Carole Goble, Ian Horrocks. 
DAML+OIL is not enough. 
SWWS-1, Semantic Web working symposium, Stanford (CA), 
July 29th-August 1st, 2001.
http://potato.cs.man.ac.uk/papers/not-enough.pdf


> 
> [...]
> >
> > > Perhaps I am missing something? Of course the other option is to edit
> your
> > > ontologies as XML and parse as RDF when needed. This is how most XML
> > > systems do things, e.g. even though XML is parsed into an internal
> object
> > > model e.g. the DOM, _editors_ don't edit the DOM, they edit the XML.
> Indeed
> > > if I were writing an ontology editor, I would edit your abstract syntax
> > > directly and then generate XML/RDF from that. I will say more about this
> > > later.
> >
> > What you are missing is that round-tripping has to end up with a knowledge
> > base that has the same extra-logical connotations (whatever they may be)
> as
> > the original knowledge base.  These extra-logical connotations may include
> > even such things as the order of definitions.
> >
> 
> Is so-called 'round trippability' a requirement? goal?
> 
> I thought that by defining the model theory _on the set of RDF triples_ that
> the so-called KBs would be in some way equivalent. Isn't that the whole
> point of this exersize?

Well, the argument here is that there is something more than logical
equivalence to be considered.  If all that we are interested in is logical
equivalence, then surface syntax becomes totally irrelevant.

> Regarding "order of definitions" this is an important point. This is why I
> feel that preserving rdf:parseType="daml:collection" is important because
> RDF as opposed to XML, does not normally preserve order. _daml:collection_
> of course does. Hence when order is important the contents should be in a
> daml:List.

Actually, RDF collections do preserve order, even when one would like them
not to.  The problem with RDF collections is thus not related to ordering
but to well-definedness and closure.

> Well, DAML+OIL already does that.

> Look, you've made a proposal to significantly change DAML+OIL. My
> understanding of the ground rules is that this would be acceptable, _if and
> only if_ there is a significant benefit. Rather than you asking _me_ to
> create some sort of proof that my point is applicable, instead I ask you for
> a simple example, written in DAML+OIL (XML format) which illustrates the
> problem. This example should be the approximately the simplest that
> illustrates the problem. If I produce a counter-example, also written in
> DAML+OIL, I would like you to explain to me why I am incorrect.

Well the round-tripping problems are addressed in the paper referred to
above, which has an example.

> I am just trying to understand the issues. On the other hand I have already
> spent at least a solid day this week on OWL and intend to spend more time
> this weekend -- I am writing up a non-XML surface syntax which is similar to
> the proposed OWL abstract syntax, yet is largely (perhaps completely)
> compatible with DAML+OIL -- in any case please send me back a simple
> concrete example which illustrates the problem, as that will be the best way
> of convincing me that a real issue exists.

The White-van-man in the paper referred to above does, I believe,
illustrate the problem.

> Jonathan

Peter F. Patel-Schneider
Received on Friday, 22 March 2002 12:50:07 GMT

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