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Re: [OPEN] and/or [PORT] : a practical question

From: Natasha Noy <noy@SMI.Stanford.EDU>
Date: Mon, 29 Mar 2004 17:56:07 -0800
Message-Id: <p06020402bc8e83dcf25e@[]>
To: Aldo Gangemi <a.gangemi@istc.cnr.it>, Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: Guus Schreiber <schreiber@cs.vu.nl>, SWBPD list <public-swbp-wg@w3.org>, Nicola Guarino <guarino@loa-cnr.it>, claudio.masolo@ladseb.pd.cnr.it

At 7:54 PM +0100 3/27/04, Aldo Gangemi wrote:
>My two cents ...

[snipping eighteen cents...]

>Bottom-line: let Natasha, Bernard, or anyone else produce cases of 
>reasonable use of metaclasses, and let's try to find an alternative 
>way to model them. If that way is unnecessarily complicated for the 
>use case we are considering, then we can consider that use an 
>example of best annotation practice.

Aldo, your bottom line assumes that it is _always_ better to avoid 
using metaclasses if there is a somewhat reasonable (but perhaps less 
intuitive, more cumbersome, but not overly so) way to represent the 
same thing without them. I think it is a strong assumption to make 
and using it as an imperative for best practices is even a stronger 
(and more dangerous) thing to do. It is already clear from the 
discussion that there is no consensus in the community. Given that, 
instead of trying to produce  documents that say "avoid metaclasses 
if at all possible", we should just acknowledge the different 
approaches and describe them. Then people can choose.

There should  be a "presumption of innocence" of any construct that 
is valid in the language. Sure, there are trade-offs. There are 
examples when using metaclasses allows for a simpler and more 
intuitive model or for easier use in application (e.g., some 
knowledge-acquisition applications; not all applications and 
reasoners on the SW are going to be DL reasoners). At the same time, 
you loose the ability to have a DL reasoner to use that information. 
And we should document that too and show ways to do it differently so 
that the ontology is in OWL DL, if that's what one needs.

As an aside, I must say that in my interactions with Protege users, 
many of those who use OWL for modeling, do it simply because it is a 
standard and never think or plan to invoke a classifier (or define 
any necessary and sufficient conditions; just necessary conditions).

>IMO, it remains to be demonstrated that there exists a case in which 
>a reasoner must be able to reason on classes and metaclasses in the 
>same problem space, without alternative solutions.

Again, this assumes that, for all reasoning services, it is always 
best to avoid metaclasses. As many have pointed out already, we don't 
have enough experience to know what kind of modeling would work on 
the SW. More important, we don't have enough real SW applications to 
know what kind of reasoning will be most pervasive and useful on the 
SW. If we try to optimize the modeling for a particular single kind 
of reasoning (e.g., DL reasoning), we may shoot ourselves in the foot 
by encouraging people to produce ontologies that real-world SW 
reasoners won't be able to use productively. I am all for Pat's 
humility stance.

Received on Monday, 29 March 2004 20:56:42 EST

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