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Re: OWL S&AS: Translation to RDF Graphs [proposed reply]

From: Dan Connolly <connolly@w3.org>
Date: 16 Jun 2003 20:09:31 -0500
To: www-webont-wg@w3.org
Message-Id: <1055812171.27168.292.camel@dirk.dm93.org>

[I took the ball on this in the 12Jun telcon...
I supplemented the issues list with a link
from issue 5.26 to Seans "Parsing OWL" as
we discussed, and I cited the "rules
of thumb" appendix.

But frankly, we're really thin on *why* we
decided what we decided re issue 5.26.
I think it comes down to: of the designs that
were available, the WG was more confident
it could finish one than the others. But
even that rationale isn't clearly justified.

So the following is the best I could come up with based
on what we've got. I don't think I'd find it
very satisfactory if I were Dave; it comes very close
to "we're tired of talking about this; go away."
1/2 ;-)
]

On Fri, 2003-05-09 at 13:33, Dave Beckett wrote:
>   OWL Web Ontology Language Semantics and Abstract Syntax
>   W3C Working Draft 31 March 2003
> 
>   4.1. Translation to RDF Graphs
>   http://www.w3.org/TR/2003/WD-owl-semantics-20030331/mapping.html#4.1
> 
> This transformation table gives the mapping from OWL's abstract
> syntax to RDF triples which means that if you have an OWL ontology in
> the abstract syntax you can write it in OWL's transfer syntax - RDF triples.
> 
> It is however more difficult to see how to go from RDF triples to
> OWL's abstract syntax.  As a semantic web technology, OWL builds on
> RDF triples (and RDF on XML for syntax, URIs etc.) and this form of
> presentation makes it harder to see how to start with RDF and gain
> from OWL vocabulary.

Discussion of whether and how to specify mappings between OWL abstract
syntax and RDF graph syntax is the subject of this issue:

  5.26-OWL DL Sytntax
  http://www.w3.org/2001/sw/WebOnt/webont-issues.html#I5.26-OWLDLSyntax

The working group discussed various alternatives, but eventually
decided, 27 March 2003, on the design in the last call document.
Note the outstanding dissent:

  5.26 OWL DL Syntax - Formal Objection
  From: Jeremy Carroll (jjc@hpl.hp.com)
  Date: Fri, Mar 28 2003
  http://lists.w3.org/Archives/Public/www-webont-wg/2003Mar/0264.html

While the points in your comment are well-made, they don't seem
to provide new information which would justify reopening
the issue.

You may be interested in continued related work, meanwhile...


> In detail:
> 
>  1) This presentation may make it hard to see how to transfer OWL -
>    from the transfer syntax (RDF triples) to the OWL abstract syntax.
> 
>    Running the (non-deterministic!) mapping rules backwards seems the
>    only way and is up to each implementer to work out how to do that.
>    Giving this mapping explicitly would be beneficial.  If it depends
>    on the OWL subset in use, this should also be described.  All of
>    this should preferably have and be linked to test cases.

You may be interested in some related work by individuals in the
working group:

Parsing OWL, Sean Bechhofer, University of Manchester, June 02 2003
http://wonderweb.semanticweb.org/owl/parsing.shtml
 
While this doesn't provide an actual specification of the reverse
mapping, it does "describe a basic strategy that could be used ...
to construct an OWL ontology that corresponds to the triples
represented in the RDF"


>  2) It is not clear from this mapping what restrictions there are on
>    any existing RDF such that it would already be legal OWL DL or OWL
>    Lite (apart from trying it out with an OWL validator).
> 
>    If the path from RDF to anything but OWL Full is not clear, it
>    seems that it is unlikely that benefits of OWL DL or OWL Lite will
>    be wholly realised.

In order to clarify the path from RDF to OWL DL,
informative section is being added to the OWL Reference:

  Appendix E. Rules of Thumb for OWL DL ontologies
  http://www.daml.org/2002/06/webont/owl-ref-proposed#app-DLinRDF


>  3) The optional and non-deterministic mappings to/from triples are a
>    bad idea that are likely to cause interoperability problems and
>    make the mappings harder.  I urge you to consider removing such
>    non-determinism.

Note that "non-deterministic" does not mean "not completely specified";
it just means "not 1-1"; i.e. one abstract syntax structure corresponds
to a number of RDF graphs. For example, for the intersection
of classes A, B, and C, it doesn't matter what order they appear
in an RDF collection.

Taken literally, your request is to specify that exactly one RDF
graph is allowed for any OWL abstract syntax structure. Could
you confirm that this is what you're suggesting? It seems unlikely.


>      I note that several of these are related to having owl:Class and
>      rdfs:Class, a separate issue.
> 
> Thanks
> 
> Dave

Please let us know if you find this response satisfactory.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Monday, 16 June 2003 21:09:06 GMT

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