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Re: class and inviduals

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Thu, 18 Nov 2010 18:58:55 +0100
Cc: Rinke Hoekstra <hoekstra@few.vu.nl>, Pavel Klinov <pklinov@cs.man.ac.uk>, Marco Colombetti <colombet@elet.polimi.it>, public-owl-dev@w3.org
Message-Id: <BB9B559A-5B91-4255-B0F1-7C530D9EBC04@inf.unibz.it>
To: Pat Hayes <phayes@ihmc.us>
I believe that in RDF there is no difference between punning and f-logic-like (or common-logic-like) semantics, since the language is too weak to be able to write sentences where the two semantics would lead to different behaviours. 
I disagree technically with Pat below that classes and objects are the *same* thing in f-logic or common-logic, if you intend a class to be a proper set. To model exactly this case you need a proper high-order logic, while f-logic or common-logic are a syntactic variant of first-order logic. Nonetheless, I am with Pat when I say that the f-logics semantics is very useful and interesting compromise in the middle.
Again, remember that, as also Michael tried to explain with the cases in DBPedia, using punning in OWL-DL leads to a substantial difference in the behaviour wrt the f-logic-like or proper high-order behaviour. 
cheers
--e.

On 18 Nov 2010, at 18:25, Pat Hayes wrote:

> 
> On Nov 17, 2010, at 4:13 AM, Rinke Hoekstra wrote:
> 
>> Hi Pavel,
>> 
>> On 16 nov 2010, at 17:50, Pavel Klinov wrote:
>>> As for OWL 2, I do agree with Enrico. Punning is a not quite a logical
>>> pattern - it's a meta-modeling feature and has to be used with care.
>>> If you pun an object X and a class X they will still be treated as
>>> separate entities by a reasoner ("X-as-class" and "X-as-individual" if
>>> you will). It can be confusing, for example, one may place a data
>>> property assertion on X (as an individual) and then wonder why other
>>> instances of X (as a subclass) do not inherit that property.
>> 
>> This is indeed what happens if you use punning. However, if you interpret it as OWL 2 Full (without punning), the inheritance wouldn't occur either. 
>> 
>> The fact that some language feature may be confusing is not a very good general argument against using it. 
>> 
>>> At the
>>> same time other tools, like Protege, may give a false impression that
>>> "these are really the same thing".
>> 
>> Hm, but for all practical purposes they *are* the same thing, they are just interpreted differently dependent on context. OWL 2 DL reasoners may separate these contexts for efficiency purposes, but an RDFS/OWL 2 Full reasoner or RDF query engine won't. 
>> 
>> This is fine if you ask me... I have yet to come across a situation where this potential confusion had any practical consequences. 
> 
> And in OWL full and RDF and ISO Common Logic, they really ARE the very same thing, with no 'punning' involved. Check out the model theory. Everything in the universe is an individual and a class and a property (and in CL, also a relation and function of every possible arity; and in IKL, which extends CL, also a proposition.) I call this style of model theory 'pollarding': every individual (logical sense) is provided *by the semantics* with enough branches - enough semantic apparatus - to play any logical role that might be required by the syntactic occurrence of its name. It is a view of the universe which says, in effect, I do not know what 'kind' of thing this entity is, so I will presume (as a matter of logic) that it might be any kind, or several kinds, of entity, and be prepared to interpret it thus. It is a kind of rigorous metaphysical agnosticism, and the logic is built on this as a fundamental principle. I feel, in fact, that this is the core of what makes FO logic truly first-order: it is the only logic which makes absolutely no ontological presumptions or constraints on the entities that it talks about. BUt no doubt this is getting to deep for an email discussion :-)
> 
> Cheers
> 
> Pat
> 
>> 
>> Cheers,
>> 
>> Rinke
>> 
>>> Apologies if I'm mistaken in my understanding of punning.
>>> 
>>> Cheers,
>>> Pavel
>>> 
>>> On Tue, Nov 16, 2010 at 3:08 PM, Pat Hayes <phayes@ihmc.us> wrote:
>>>> 
>>>> On Nov 16, 2010, at 4:22 AM, Marco Colombetti wrote:
>>>> 
>>>>> Aldo is right, punning is allowed in OOWL2, but I wonder whether it should be considered as good practice. In my opinion it conceils certain important modelling choices, and is likely to induce confusion.
>>>>> 
>>>>> Any strong opinion about this?
>>>> 
>>>> Yes, one strong opinion: it is VERY good practice. The ISO Common Logic framework goes slightly further, allowing any 'thing' to be treated simultaneously as an individual, a class or a relation ('property') of any number of arguments; and we have found in many applications that the resulting freedom to express ontological decisions independently from the apparent constraints of the logic is more than 'good' : it represents a quantum jump in ontology engineering.
>>>> 
>>>> The key point is that 'individual' in a metaphysical sense is one notion, whose merits can be debated; but 'individual' in the logical sense is quite another. The latter means simply 'a member of the universe of discourse' or 'within the scope of quantification'. The traditional 'good practices' typically get these two distinct notions confused, and use syntactic constraints arising from the latter to model the former, to the lasting detriment of good ontological engineering.
>>>> 
>>>> Pat Hayes
>>>> 
>>>>> 
>>>>> Marco
>>>>> 
>>> --pavel
>>> http://www.cs.man.ac.uk/~klinovp
>>> 
>> 
>> 
>> ---
>> Dr Rinke Hoekstra
>> 
>> AI Department         |   Leibniz Center for Law    
>> Faculty of Sciences   |   Faculty of Law            
>> Vrije Universiteit    |   Universiteit van Amsterdam
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>> +31-(0)20-5987752     |   +31-(0)20-5253497         
>> hoekstra@few.vu.nl    |   hoekstra@uva.nl           
>> 
>> Homepage: http://www.few.vu.nl/~hoekstra
>> 
>> 
>> 
>> 
>> 
>> 
> 
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Received on Thursday, 18 November 2010 17:59:33 GMT

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