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Re: vass-01 flat layering

From: Graham Klyne <gk@ninebynine.org>
Date: Sat, 24 May 2003 19:46:19 +0100
Message-Id: <>
To: Brian McBride <bwm@hplb.hpl.hp.com>, rdf core <w3c-rdfcore-wg@w3.org>

At 13:12 24/05/03 +0100, Brian McBride wrote:

>Danbri and I have been discussing issue:
>   http://www.w3.org/2001/sw/RDFCore/20030123-issues/#vass-01
>Its quite hard to get a crisp quote of the problem from the email thread 
>but I think the issue is that schema does not layer the same way as, say 
>UML, in that classes can be members of themselves and one can take a 
>subproperty of subPropertyOf or rdf:type.
>I think we need to clearly articulate the advantages of the design choice 
>that has been made.

I'm not convinced of a *need* to do this.  (But if we can, then fine...)

I think the main issue here is that the non-layering is a fundamental 
feature of the RDF we were tasked to clarify.  I think we don't really have 
any discretion to consider other design approaches.

>I suggest the following reason for the design choice and why we should not 
>change.  I welcome comments and other suggestions:
>1) RDFS is designed to be a lower layer for the semantic web stack that is 
>extended by restriction.  All structure at this layer is imposed on all 
>higher layers.  A layered structure is not necessary and the principle of 
>minimal restriction suggests it should be omitted.
>2) A further consideration is the cost of change at this point.  To switch 
>to a layered approach would require a massive rethink and would affect not 
>only the RDFCore specs but also OWL.  Only a show stopping problem with 
>the current design could justify the cost of such a change.

This might be underscored by mentioning the large number of implementations 
that currently depend on this model (esp schema uses where rdfs:Class is 
treated as both resource and class, and is a member itself, etc.).

>We note that it is possible to build more strictly layered languages on 
>top of RDF(S), Owl DL/Lite being examples.

A good point to make, I think.


Graham Klyne
PGP: 0FAA 69FF C083 000B A2E9  A131 01B9 1C7A DBCA CB5E
Received on Sunday, 25 May 2003 05:16:16 UTC

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