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

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 14 May 2003 13:06:07 -0400 (EDT)
Message-Id: <20030514.130607.14953644.pfps@research.bell-labs.com>
To: www-webont-wg@w3.org

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Subject: OWL S&AS: Translation to RDF Graphs
Date: Fri, 09 May 2003 19:33:00 +0100


Thank you for your comments.

>   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.
> 
> 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.

A normative definition of this is very likely to be no more intelligible
than the current sitation.  A non-normative and incomplete, but more
comprehensible discussion would be useful.  The Guide
(http://www.w3.org/TR/owl-guide/ serves as at least a partial vehicle for
this purpose.

>  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.

Agreed, but the Guide serves this purpose.

>  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.

There are at least the following sources of non-determinism

1/ Optional rdf:type triples.
   These mostly serve the purpose of allowing existing RDF documents to be
   augmented with more information and thereby made into OWL DL documents,
   as in 
        ....
	foo rdf:type rdf:Property .
	....
	foo rdf:type owl:AnnotationProperty .

2/ Allowing for only a skeleton of owl:sameIndividual, owl:differentFrom,
   owl:equivalentClass, owl:disjointFrom, etc., triples to be present, as in
	ex:a owl:differentFrom ex:b .
	ex:b owl:differentFrom ex:c .
	ex:c owl:differentFrom ex:d .
	ex:d owl:differentFrom ex:a .
	ex:d owl:differentFrom ex:b .
	ex:d owl:differentFrom ex:c .
   This allows for more flexibility.

3/ Multiple ways of providing distinct individuals in the triples.
   Fixing this would require a special syntax in the abstract syntax for
   AllDifferent.

All these have utility.  Removing them would result in fewer OWL DL and OWL
Lite graphs, and would remove some graphs that can be imagined to be
naturally produced.  

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


Please reply to this message indicating whether anything more needs to be
done in this area.

Peter F. Patel-Schneider
Bell Labs Research
Lucent Technologies
Received on Wednesday, 14 May 2003 13:06:15 GMT

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