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horst-01 - after hours discussion

From: Jeremy Carroll <jjc@hpl.hp.com>
Date: Fri, 20 Jun 2003 19:25:37 +0200
To: w3c-rdfcore-wg@w3.org
Message-id: <BHEGLCKMOHGLGNOKPGHDOEMHCBAA.jjc@hpl.hp.com>

This is a *scribe* report on the after hours discussion.
I am not expressing a personal opinion on the content here.


After hours of telecon today, the determined few (I think DanC, PatH,
Jeremy, JanG, DanBri) kept going for longer, discussing the complexity of
the 12a and 12b rules added to address horst-01 (one of the AOB items!).

A different possible design (to that in the editor's draft) was discussed.

The current design has extensional definitions of subClassOf and
subPropertyOf.

http://www.ihmc.us/users/phayes/RDF_Semant_Edit_appenda.html#rdfs_interp
[[
<x,y> is in IEXT(I(rdfs:subClassOf)) if and only if x and y are in IC and
ICEXT(x) is a subset of ICEXT(y)

<x,y> is in IEXT(I(rdfs:subPropertyOf)) if and only if x and y are in IP and
IEXT(x) is a subset of IEXT(y)
]]

This could be changed to intensional definitions
[[
If <x,y> is in IEXT(I(rdfs:subClassOf)) then x and y are in IC and ICEXT(x)
is a subset of ICEXT(y)

If <x,y> is in IEXT(I(rdfs:subPropertyOf))then x and y are in IP and IEXT(x)
is a subset of IEXT(y)
]]

transitivity and reflexivity can be achieved by fiat:
e.g.

[[
IEXT(I(rdfs:subClassOf)) and IEXT(I(rdfs:subPropertyOf)) are
transitive and reflexive.
]]
(in the green box)

There was discussion of whether it is useful to have rdfs:Resource as the
maximal class. If yes, then this too, would have to be declared by fiat in
the model theory. It was suggested by Pat that declaring conditions by fiat
was distasteful. (Note the current truth of transitivity, reflexivity and
rdfs:Resource as maximal all follow from the extensional reading of
rdfs:subClassOf - thus any of these features we wish to maintain has to be
explicitly added to the MT).

The section 4.1
http://www.ihmc.us/users/phayes/RDF_Semant_Edit_appenda.html#ExtensionalDomR
ang

would be retitled, to "Extensional RDFS" or something like that, and permit
semantic extensions to add back in the extensional reading of subClassOf and
subPropertyOf.


====

The rationale for such a change comes in the entailment rule appendix.

The bizarre rules rdfs12a and rdfs12b would no longer be needed, since their
validity depends on the extensional reading of subClassOf.

They would hence be moved from the main RDFS section to the variant at the
end (with rdfs2a rdfs3a rdfs4a' and rdfs4b'). Moreover, the completeness fix
I noted in my review would then be added to the only occurrence of these
rules.

Since these rules are a significant obstacle to complete implementation of
RDFS, dropping them to the optional extras section, is an advantage.

Jeremy
(I believe that Pat and Dan were the only others left, when we decided to
minute the after hours discussion).
Received on Friday, 20 June 2003 13:26:07 EDT

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