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Re: Layering on the Semantic Web

From: Dan Connolly <connolly@w3.org>
Date: 03 Jan 2002 10:58:08 -0600
To: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>
Cc: www-webont-wg@w3.org
Message-Id: <1010077088.3382.0.camel@dirk>
On Thu, 2002-01-03 at 09:46, Frank van Harmelen wrote:
> 
> In various emails to the Working Group, and also in various off-line conversations, a number of people have become very worried about the layering of OWL on top of RDF and RDF Schema. 
> 
> The problems can be summarised as follows:
> - RDF is not well suited as syntax carrier:
>   - the problems that Peter has identified with "additional" tuples 
>     (which specify only syntax) ending up in the RDF model and breaking the inference

Those "additional" tuples are a suggestion from PatH
to RDF Core that the RDF Core WG has not yet decided
on. I, for one, don't agree that they are/should-be
part of RDF.

>   - problems with scoping

scoping in RDF is quite simple, no?

>   - its inability to constrain the syntax adequately
>     (e.g., the problem with strange combinations of restrictions
>      which is responsible for much of the ugly DAML+OIL syntax).

I'd rephrase this as: the awkwardness of dealing with n-ary
(as opposed to binary) relationships.

>   - general unreadability by human processors
> - RDF Schema has some unconventional features in its meta-model. 
>   These were left out of DAML+OIL to keep the language simple, 
>   well understood on formal grounds and non-controversial, 
>   and now threaten to creep back in again. 

Which features? In what way were they left out of DAML+OIL?

The axiomatic semantics of DAML+OIL specifies all of RDFS, no?

I know the model-theoretic semantics for DAML+OIL doesn't
cover all of RDFS, but that's a limitation of the mt-semantics,
not a limitation of DAML+OIL, no?

I think this is the heart of the matter, and I very much
disagree that the layering of RDFS is a "mistake",
as claimed in

  Metamodeling Architecture of Web Ontology Languages
  Jeff Pan, Ian Horrocks
  http://www.semanticweb.org/SWWS/program/full/paper11.pdf
  <- 
http://www.semanticweb.org/SWWS/program/index.html



> Our conclusion is that these problems are much harder to solve than originally anticipated.
> Therefore, we propose to take another route for specifying the syntax of OWL:
> 
> 1. the syntax of class and property definitions in OWL (the ontology) is specified in XML

I see this as a request to change our charter. I'm not convinced
we should do this.

> 2. this is done in such a way that RDF can be used to specify instances of the ontology
> 3. we try to do 1. in such a way that significant parts of RDF Schema 
>    end up as a sublanguage of OWL 
> 
> The advantage of using XML

Note that we're already using XML by using RDF.


>
 are both technical and (not unimportant) also political:
> - XML is well suited for specifying syntax (in fact, that is its main goal in life)

Please be more clear. Do you mean XML DTDs? or W3C XML Schema?

> - it comes with a host of additional technology and standards that can then be exploited
>   for OWL (XLink, XPointer, XPath, XQuery, XSLT, etc)
>   (we can think of useful applications for all of these)

I use those with RDF every day, since "RDF is an XML text format"
	-- http://www.w3.org/XML/1999/XML-in-10-points


> - it will make our work immediately relevant to all of the XLM community. 

Our work is already immediately relevant to all of the XML community.
cf

RDF update: Query, XTM, Web Ontology and RDF Core
3 Sep 2001 | RDF | Edd Dumbill
A round-up of recent developments in the RDF and Semantic Web world.

W3C Web Ontology WG is open for business
15 Aug 2001 | W3C | Gabe Beged-Dov
Dan Connolly announced that the W3C Web Ontology (WebOnt) WG is open in
a message to the rdf-logic mailing list.

 -- http://www.xmlhack.com/search.php?q=webont&s=Search

plus

  http://xml.coverpages.org/xmlAndSemanticWeb.html

etc.

>   They share many of our goals, but there is a constant danger that they 
>   will use different (XML-based) technology, instead of RDF based technology.

RDF *is* an XML-based technology.


> RDF is still being used for what its good at: specifying ground data-structures (the "Abox" of old). 
> 
> Whether 3 is achievable or not must be investigated.
> If it is achievable, RDF Schema will not be a sublanguage of OWL, but parts of it will be. 
> 
> We suggest that this proposal is discussed at the face-to-face meeting. We will try to have a concrete proposal for (1) on the table before then. It will be helpful if we can get reactions on this proposal well before then (ie. now:-). 
> 
> Ian Horrocks,
> Peter Patel-Schneider,
> Frank van Harmelen.
>    ----

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 3 January 2002 11:58:04 GMT

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