"The way I try to explain it to business domain folks is that if something
walks like a duck, quacks like a duck and swims like a duck then it is a
member of the set of all things that are a duck. Assuming of course that
there is a class of things in the ontology with the properties "walks like a
duck" etc." (01)
Then anybody able to imitate could be a duck. (02)
I mostly support your comments, especially touching the business issues.
But even allowing that the human minds are usually tempting to simplify
things, the above is still misleading. (03)
For everybody looking for the ontological and semantic fundamentals, I much
recommend reading or rereading carefully the Topics, a blue-chip, priceless
source of learning on ontological and logical reasoning.
According it, there are five types of the logical universals (predicates or
predicables and attribution or predication), making any generic
propositions, like "A is B":
definition (or species or subclass), signifying a thing's essence;
genus or class;
accident, temporary or relative property (like as the OWL property).
In every true proposition of the above universal type, the predicate might
have the following attributes:
1. it indicates the essence of a thing and convertible (a definition);
2. it is convertible without stating the essence ( a property);
3. it is not convertible but state the essence (a class or differentia);
4. it is neither convertible nor stating the essence.
An example, how to find out a property of being a man, what is convertible
without stating the essence: "if A be a man, he is capable of learning
grammar, and if he be capable of learning grammar, he is a man."
There are the Porphyry's examples of predicable relationships:
the subject (man):
class (genus) - animal;
differentia - rational;
property - risible;
accident - white or black or yellow or red.
Chose any other subject, and try the same universal method for your duck as
----- Original Message -----
From: "Mike Bennett" <mbennett@xxxxxxxxxxxxxxx>
To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
Sent: Tuesday, April 28, 2009 2:28 PM
Subject: Re: [ontolog-forum] Last Call: OWL 2 and rdf:text primitive
> Thanks John, that makes a lot of sense.
> The way I try to explain it to business domain folks is that if
> something walks like a duck, quacks like a duck and swims like a duck
> then it is a member of the set of all things that are a duck. Assuming
> of course that there is a class of things in the ontology with the
> properties "walks like a duck" etc.
> John F. Sowa wrote:
>> Jonathan, Mike, Pavithra, and Ed,
>> As I said before, my primary concern was to clarify some confusion
>> about the use of the word 'class'. It is sometimes used as a
>> synonym for 'set', sometimes for 'type', and sometimes in a way
>> that is not clearly one or the other.
>> But I admit that the word 'class' has long been used in various ways
>> in various systems and that trying to get people to stop using their
>> favorite terminology is not easy. Therefore, I suggest that the
>> following convention be used to define the notion of class in
>> whatever system happens to use the word 'class':
>> 1. If in system X, the identity conditions for a class are
>> determined by extension, then a definition of class in X
>> should begin with a phrase similar to the following:
>> "Every class in system X is a set such that...."
>> 2. If in system X, the identity conditions for a class are
>> determined by intension, then a definition of class in X
>> should begin with a phrase similar to the following:
>> "Every class in system X is a type such that...."
>> This convention would allow people to continue to use the word
>> 'class' whenever they feel the urge to do so, but it would clearly
>> specify whether a class is considered as a set or as a type.
>> Some detailed comments on previous comments:
>> JR> Regarding OWL's choice of 'type' vs. 'class', what one needs to
>> > know is that RDF already had a notion of "type" when OWL started
>> > making overtures, so when OWL DL came to be embedded in RDF, a
>> > different term was needed, because there were RDF "types" that
>> > were not OWL "classes"...
>> That indicates that both RDF types and OWL classes are defined by
>> intension (some rule or description rather than a set of instances).
>> That would imply that every RDF type is a type, and every OWL class
>> is a type.
>> Given the convention above, you could say something along the
>> following lines:
>> Every OWL class is a type of entity specified by a document
>> identified by a particular URI.
>> MB> I seem to recall that in OWL1, a Class could be understood both
>> > as extensional (a set of individuals) and intensional (a class has
>> > a collection of properties which would define the members of the
>> > set, i.e. all individuals which have those properties are seen as
>> > members of that set - so still effectively a set of individuals,
>> > but arrived at differently).
>> In linguistics, there is a general principle that the intension
>> of a word (informally, its "meaning") determines its extension.
>> For example, the intensional definition of 'integer' or 'cow'
>> determines the set of all integers or the set of all cows.
>> If an OWL class is defined as a type, then the set of all entities
>> of that type would be the set of instances of that class.
>> PK> ... if you remove that word, it would create a gap from modeling
>> > to implementation in software world!
>> My modified recommendation above provides an option for continuing
>> to use the word 'class' whenever people prefer to use that term.
>> But it provides a way of stating explicitly whether a class is
>> considered as a set or as a type.
>> EB> The percentage of computer science graduate students who are
>> > incapable of searching the literature that is not available online
>> > in PDF form must now be well over 75%, judging from the papers
>> > I have read.
>> Not only students, but professors as well. The citation statistics
>> now indicate that for papers published in the same year, the
>> average number of citations for papers available online is 10 times
>> the number for papers available only on paper.
>> EB> ... the concept of abstract types in programming languages goes
>> > back to 1967 and Simula, and I have not been able to identify any
>> > earlier published programming language that has a formal concept
>> > of abstract type (including a search of Jean Sammet's survey,
>> > published in 1968-9).
>> Jean Sammet was not inclined toward formal definitions. Steve Zilles
>> has a good bibliography of the work in the 1960s and early '70s:
>> Before he went back to MIT, Steve and I had been designing an
>> interesting system, but it was declared to be "too difficult" for
>> the IBM Endicott engineers to understand. That was probably true.
>> I started scanning in our specification manual from March 1971:
>> EB> And therefore, unlike John, I can't fault software engineering
>> > for having chosen "class" as the term for "abstract type",
>> > regardless of the usage in other disciplines.
>> As I said above, I modified my recommendation to let people continue
>> to use their favorite terminology, but still clarify whether they
>> mean the word 'class' as a set or as a type.
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