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At 8:56 AM +0200 5/13/08, Jakub Kotowski wrote:
Patrick,
Patrick Cassidy wrote:
>
> But I haven't seen examples of the problem you
refer. Can you provide
> examples that were actually caused by multiple inheritance rather
than
> simple errors in some instance of assigning subtype per se?
>
Maybe it is necessary to say what is meant by an error. Multiple
inheritance could cause *problems* if one needed to divide the
ontology
into multiple modules. I think that is
why Alan Rector et al. developed
their normalisation technique [1] in the OpenGalen project. It
doesn't
say that you can't use multiple inheritance
Indeed, it explicitly uses it.
but rather that you should
build a kind of taxonomy "backbone" with only
single-inheritance and
then build upon it.
It says that you should have taxonomy backboneS, plural.
What the paper says is that you should separate multiple
inheritance into separate 'modules' each with single inheritance. As
it also remarks, this is a perfectly general technique which can
always be done (speaking mathematically: in fact, the technique
mentioned by John Sowa in this thread provides the necessary
mathematical foundation, if anyone is interested.) The paper
also reports on considerable experience showing that people find this
easier to deal with, which is not surprising. But none of this is
relevant to any argument about the merits of single versus
multiple inheritance: Rector's techniques are one way to approach
multiple inheritance.
Pat
Jakub
[1] Alan L Rector, Modularisation of Domain Ontologies Implemented
in
Description Logics and related formalisms including OWL
http://www.cs.man.ac.uk/~rector/papers/Modularisation-normalisation-rector.pdf
> Pat
>
> Patrick Cassidy
> MICRA, Inc.
> 908-561-3416
> cell: 908-565-4053
> cassidy@xxxxxxxxx
>
>
>> -----Original Message-----
>> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx
[mailto:ontolog-forum-
>> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Alan Ruttenberg
>> Sent: Monday, May 12, 2008 11:16 PM
>> To: bfo-discuss@xxxxxxxxxxxxxxxx; Phillip Lord
>> Cc: [ontolog-forum] ; obo-relations@xxxxxxxxxxxxxxxxxxxxx
>> Subject: Re: [ontolog-forum] [bfo-discuss] Re: Heterarchy &
Hierarchy,
>> oh my my
>>
>> On May 6, 2008, at 11:54 AM, Phillip Lord wrote:
>>>>>>>> "Alan" == Alan Ruttenberg
<alanruttenberg@xxxxxxxxx> writes:
>>> Alan> I've seen the disadvantages of
multiple asserted
>>> inheritance when
>>> Alan> reviewing, e.g. the Cell ontology in
OBO, where it was
>>> demonstrated
>>> Alan> (by the authors) that it was quite
easy to find mistakes of
>>> the sort
>>> Alan> where all of the properties
described in the definition of
>>> (multiple,
>>> Alan> and transitive) superclasses were
not true of instances of
>>> the class
>>> Alan> in question. Regarding (c) what is
perhaps being referred
>>> to is that
>>> Alan> if one practices
"normalization" in the sense that Alan
>> Rector
>>> Alan> proposes [1] then the component
single inheritance
>>> ontologies from
>>> Alan> which more complex terms are
constructed are more likely to
>>> be able to
>>> Alan> be reused by other projects.
Certainly that's the intention
>> of
>>> Alan> creating and using PATO. I've found
the exercise of factoring
>>> Alan> definitions in this manner is often
helpful and is
>>> conducive to
>>> Alan> helping the sorts of people I work
with think carefully when
>>> Alan> constructing ontologies.
>>>
>>> I think that we need to be clear here; there is a
fundamental
>>> distinction
>>> between normalisation as according to Alan Rector and to
the idea
>>> of single
>>> inheritance is a correct reflection of reality.
>> I think I've been clear on this. What I consider interesting
is that
>> the same conclusions about the pragmatics of ontology
construction
>> arise from two different approaches. For me, since I have
respect for
>> the purveyors of these two
approaches, this strengthens the case that
>> this is a good way to go about doing things.
>>
>>> While you are correct that allowing multiple inheritance
increases
>>> the risk of
>>> some common errors, it also allows modelling that is not
possible
>>> otherwise;
>>> in particular it can be used to avoid a combinatorial
explosion of
>>> terms.
>> Example?
>>
>>> My take; single inheritance can be easier and simpler
sometimes,
>>> but not always;
>> Curious about the not always. And not sure about the easier
or
>> simpler either. "I would have written a shorter letter
if I had
>> time", etc. But I think it leads to better quality
results.
>>
>>> using a computationally amenable languages and
normalisation allows
>>> you to get some of the advantages of both.
>> +1 on that one.
>>
>> -Alan
>>
>> (the *other* Alan R ;-)
>>
>>> Phil
>>>
>>>
>>>
>>> ps, I started of writing this email referring to Alan
Rector as
>>> "Alan". Then I
>>> had to correct it to "Alan R" to disambiguate
from you. Then again.
>>> Eech.
>>
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