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Re: [Fwd: SIG2 Amsterdam meeting - summary]

From: GUIDO VETERE <gvetere@it.ibm.com>
Date: Thu, 10 Jan 2002 11:03:40 -0500 (EST)
To: Nicola Guarino <Nicola.Guarino@ladseb.pd.cnr.it>
Cc: Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>, Mike Dean <mdean@daml.org>, www-archive@w3.org
Message-ID: <OF20A573BC.4F7578EF-ONC1256B3B.003EAB6A@italy.ibm.com>

Hi Nicola,
thank you for getting involved in this discussion. You are right: 'part'
can be considered (and is generally considered indeed) by a pure formal
perspective, as a relation carrying a specific meaning axiom (weak
supplementation) and (at least) asymmetry and antireflexivity. From this
standpoint, 'part' does not depend upon the context, thus is eligible as
keyword for the ontology definition language.

Nonetheless, time-space locations cannot be part of objects, concrete
objects cannot be part of abstract objects, sortal objects cannot be part
of non-sortal objects, etc. That's what I had in mind when I said that the
usage of 'part' is affected by the context. Consider also that, while
'part' supplies an identity criterion for 'extensional' classes, this is
not true for 'intensional' classes. This is, in my opinion, a noticeable
difference. Are we sure that, when we say <'hour' part of 'day'> and
<'wheel' part of 'car'> we are using the same 'part' relation ? My (naive)
impression is that talking about 'part' is actually talking about a certain
class of relations carrying weak supplementation, asymmetry, etc. Yet, a
lot of relations would fall into this class (consider 'cooperate',
'coexist', and all the verbs tagged with 'co-') that are not (at least
intuitively) considered as 'part' relations. Here I see a difficulty...

Besides this discussion, introducing 'part' as a keyword in the ontology
definition language would either imply the adoption of a large number of
other keywords (including 'abstract', 'extensional', 'sortal') or open to
language-driven semantic inconsistencies. That's the reason why I  would
avoid this choice at all.  On the other hand, introducing 'transitive',
'symmetric', etc.., as modifiers for any binary relation would allow a
pretty good formalization of the different kinds of part-of relations at
the model level (e.g. a standard top-level ontology), where domain-range
constraints can be suitably set.

Finally, I insist on the need of introducing 'type' vs. 'role' as modifiers
for class declarations. This distinction (that I learned from your works)
woud be crucial for for many practical reasons. Have you any comment on
that ?

Kind regards,
Guido Vetere
IBM SWG Rome Labs.

Nicola Guarino <Nicola.Guarino@ladseb.pd.cnr.it> on 08/01/2002 10.35.24

To:   Frank van Harmelen <Frank.van.Harmelen@cs.vu.nl>, Mike Dean
cc:   Guido_Vetere@tivoli.com, www-archive@w3.org
Subject:  Re: [Fwd: SIG2 Amsterdam meeting - summary]

At 1:19 AM +0100 19/12/01, Frank van Harmelen wrote:
>Mike (Cc Guido and Nicola),
>Below input from Guido Vetere on suggestions for the Web Ontology
>language, as input for the January meeting of the Working Group.
>He raises some very interesting issues not raised by others before:
>- whether other relations then "subclassOf" (such as "partOf")
>should be included in the language (he argues cogently why not).
>- He does argue to introduce some other distinctions, though. In
>particular between "essential" and "non-essential" roles.
>(I believe this is closely connected to the remarks by Dan Brickley
>on time-varying roles, in his recent message to the WebOnt group at
>- the need for better supporting natural-language "names" for the
>objects in the language than is currently available in RDF.
>(Guido, Nicola: Mike has taken over my role to collect input for the
>meeting, which is why I forward your contribution to him).
>    ----
>-------- Original Message --------
>Subject: SIG2 Amsterdam meeting - summary
>Date: Tue, 11 Dec 2001 16:56:54 +0100
>From: Guido_Vetere@tivoli.com
>To: Frank.van.Harmelen@cs.vu.nl
>CC: Nicola.Guarino@ladseb.pd.cnr.it
>Hi Frank,
>here is a brief summary of my remarks on the SIG2 meeting, to be used as
>input for the W3C ongoing discussions.
>1 - Modeling 'part' relations: formal vs substantial features (whether the
>ontology language should include the 'part' relation or not).
>In my opinion, although mereology is a very formal theory, 'part' is not a
>formal relation itself. In fact, its meaning depends on the 'particulars'
>it applies to: sortals, material entities in general, collections,
>space-time locations, and so on.  As a formal language, the W3C ontology
>syntax should avoid the introduction of such non-formal elements.

Hi Guido,

 sorry for this late feedback. I must say I disagree with this
view: the part-of relation is in my opinion a "formal" relation, in
the precise sense that it does not imply any constraints on its
arguments: you can have parts of ideas, parts of objects, parts of
events... In all these cases, I believe there is a common meaning of
the notion of "part", which corresponds to a minimal set of axioms:
part-of is intended as a partial order (asymmetric, antireflexive,
transitive), plus the so-called "weak supplementation" axiom, which
says that if x is a proper part of y then some z must exist, which is
als a proper part of y but it is different from x. This corresponds
to what Peter Simons says at the end of his seminal book "Parts - A
study in ontology" (Clarendon Press 1987). I quote below a
significant passage (p. 363):

"If this is all there essentially is to the part-of relation, why can
stronger principles sometimes apply? The answer lies not in the
part-relation itself but in the nature of the objects to which it

An important case of a specialized part-of relation is the member-of
a member of a collection is a special part of the collection, which
exhibits a peculiar property: unity. This is why member-of is not
transitive, while part-of is. Again, however, member-of is a formal

Nicola Guarino
National Research Council       phone: +39 O49 8295751
LADSEB-CNR                      fax:   +39 O49 8295763
Corso Stati Uniti, 4          email: Nicola.Guarino@ladseb.pd.cnr.it
I-35127 Padova

(***updated 19/12/2001 ***)
Received on Monday, 14 January 2002 00:45:55 UTC

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