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Re: SEM: 5.5 List semantics

From: pat hayes <phayes@ai.uwf.edu>
Date: Wed, 30 Oct 2002 22:40:37 -0600
Message-Id: <p05111b3fb9e660f26054@[]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: www-webont-wg@w3.org

>I PROPOSE that OWL augment the characterization of the RDF List vocabulary
>so that it serves the needed purpose for OWL.   The technical details for
>this augmentation can be found in
>   http://www-db.research.bell-labs.com/user/pfps/owl/rdfs.html
>I PROPOSE that there be no owl:List, owl:first, owl:rest, or owl:nil.

That won't work. The proposed semantics for the RDF list vocabulary 
is an empty semantics. There will be no restrictions on lists: they 
can have multiple heads, forking tails, rdf:nil can have countably 
many rdf:rest properties. All manner of 'impossible' things will be 
allowed. The resulting structures will bear no semantic or syntactic 
relationship to Lisp-style lists in the usual sense at all: they will 
be arbitrary graph structures linked by the list vocabulary names in 
arbitrary ways. Recursive algorithms will not work on them.

In order to use this coherently in OWL we will still need owl:List (a 
subclass of rdf:List, analogous to owl:Thing a subclass of 
rdf:Resource) and owl:nil (distinct from rdf:nil, which can be in the 
domain of rdf:rest and hence cannot be used as an end-of-list marker 
in OWL), and we will need to essentially axiomatize Sexpressions in 
OWL. So the OWL list vocabulary will be, at best

owl:List rdf:first rdf:rest owl:nil

which it seems to me is a bad decision on almost all grounds. Im not 
even sure if we can use rdf:first and rdf: rest, since other 
applications might consistently assume that a list can have, say, 
three rdf:firsts; that would be consistent with the proposed RDF 
specs. It is a violation of the RDF spec for OWL to impose extra 
meaning on something in the RDF namespace, so OWL should use its own 
properties and subproperty them to the RDF list properties.

I therefore PROPOSE instead that OWL totally ignore the RDF list 
vocabulary, which will not have a semantics adequate for OWL 
purposes, and instead revert to using its own list vocabulary.

>I maintain that this sort of augmentation is entirely in keeping the
>entirely of the RDF(S) philosophy.

It would be if it could be made to work, but I do not believe it can be.


PS. I have BCCd this message to the RDF core WG for information purposes.

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Received on Wednesday, 30 October 2002 23:41:27 UTC

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