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Re: early incomplete draft of semantics document

From: Jos De_Roo <jos.deroo.jd@belgium.agfa.com>
Date: Tue, 20 Aug 2002 00:57:20 +0200
To: pat hayes <phayes@ai.uwf.edu>
Cc: Guus Schreiber <schreiber@swi.psy.uva.nl>, www-webont-wg@w3.org
Message-ID: <OF6CD7EFD7.15F16D95-ONC1256C1A.007CABD1@agfa.be>

> There is a very incomplete draft of the document I promised to write at
>
> http://www.coginst.uwf.edu/users/phayes/RDFS2OWL.html
>
> I will be updating it over the next few days at irregular intervals,
> but the basic outline shouldnt change much.
>
> Any feedback would be welcome. There are a couple of places,
> indicated by comments, where Im not entirely sure that the MT is
> right, but I have followed Peter's semantics in any case.

[...]

> In a sharp contrast to RDF(S), classes and properties are
> not first-class entities in OWL: they cannot be in the
> domain and range of properties, or be contained in classes.
> In fact the OWL universe is even more restricted than figure
> 4 illustrates, since OWL properties (which may apply only to
> things) may have values which are things or datatype values,
> but not both, giving a parallel distinction between two kinds
> of property.

this is simply a different design than RDF(S) and the
SW design as elaborated in http://www.w3.org/DesignIssues
so please let's first of all resolve that "sharp contrast"

[...]

> 3. Skirting paradox: Inconsistencies in OWL/RDF
> @@ discussion of the 'Peter paradox'. Different views on
> how to treat it, and whether it should be considered to be
> pathological. Semantic analysis in GHOWL. Imposing extra
> 'global' syntax restrictions to enforce tree-structured graphs.
> Conclusion: using a recursive syntax certainly avoids such
> nasties, but they are not fatal; if one wishes to stay in the
> RDF world, it is possible without incurring paradoxes. @@

that is definitely good news

> 5. Injecting syntax into semantics.
> While the semantic conditions described above faithfully
> capture the appropriate meanings for the OWL abstract
> syntax when rendered into RDF, it is clearly less elegant
> to have conditions stated in terms of entire subgraphs rather
> than on a triple-by-triple basis. For example, this requires
> inference engines to 'assemble' entire subgraphs in order to
> draw conclusions, and it provides no meaning to well-formed
> RDF graphs which have incomplete OWL subgraphs, eg incomplete
> lists or partially formed restriction triplets. Moreover,
> ghowl-entailment cannot be defined in terms of closure rules
> and rdf-entailment.

I'm not completely understanding this paragraph and in
particular it's last sentence
(as a matter of implementation fact, we do *both* assembly
of function trees and their triple assertions and when the
former is not giving unifiers the latter mostly do)

-- ,
Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/
Received on Monday, 19 August 2002 18:58:02 GMT

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