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

From: Aldo Gangemi <a.gangemi@istc.cnr.it>
Date: Wed, 31 Mar 2004 08:50:41 +0000
To: Natasha Noy <noy@SMI.Stanford.EDU>
Cc: Ian Horrocks <horrocks@cs.man.ac.uk>, 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
Message-id: <1080723041.406a8661253e1@imp.rm.cnr.it>

Hi Natasha,

frontline: I am not for the pride stance :)))

I do not want to recommend avoidance of metaclasses in general.
I think there exist more than two positions in most group discussions.
In this case, my position is a "qualified" agreement for best practices in the 
use of metaclasses (annotations, real metaproperties, etc.), together with an 
agreement on documenting worst practices in the use of metaclasses.

At 17:56 -0800 29-03-2004, Natasha Noy wrote:
>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 

No, you are overinterpreting me. If avoiding metaclasses is less intuitive and 
cumbersome, it is not reasonable to put the burden on the shoulders of a na´ve 
I only suggest to describe *alternative* ways. These can then be used directly 
by the modeller if they have a comparable intuitiveness, otherwise can be used 
to generate mappings with appropriate tools, or simply suggested as 
alternatives (not better alternatives), in order to stay within OWL-DL.

>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.

This is similar to what I suggested, I never use "imperatives" nor "avoid x if 
at all possible". But you (or Pat?) seem to imply that, since there is no 
consensus, then we cannot even *talk* or *propose* alternatives on grounds that 
are not just registering the uses of a community.

>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.

Ah, OK, so we agree.

>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).

From my interaction with users, I should say that many interesting applications 
(actually, the most interested parties come from industrial applications) need 
classification, and necessary/sufficient conditions.
OTOH, my main point was not in order to defend OWL-DL (there are other 
champions for that), but to witness the existence of other modelling practices, 
which have certain nice properties.

>>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.

Did I say that?!!! I intended that, from a scientific viewpoint, there is no 
stringent evidence that reasoning on metaclasses in the same problem space is 
*unavoidable* for the Semantic Web. 
This position has not much to do with best practices (let alone the foundations 
of mathematics!), it was just a comment from me as a researcher rather than a 
recommender or registrant of common uses (if every scientist just acts like 
that, no real progress could be envisaged ...).

>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.

New bottom-line: dear father and mother, I vouch for my humility.

Aldo Gangemi
Research Scientist
Laboratory for Applied Ontology
Via Nomentana 56, Rome, Italy

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