W3C home > Mailing lists > Public > semantic-web@w3.org > August 2008

Re: Thing and Class

From: Jie Bao <baojie@cs.rpi.edu>
Date: Wed, 27 Aug 2008 21:29:51 -0400
Message-ID: <b6b357670808271829v182c367fu67cdb8b3bcc98ed5@mail.gmail.com>
To: "Harry Halpin" <hhalpin@ibiblio.org>
Cc: "Richard H. McCullough" <rhm@pioneerca.com>, "Jack Krupansky" <jack@basetechnology.com>, "Semantic Web at W3C" <semantic-web@w3.org>

Harry, I guess you mean this book?



On Wed, Aug 27, 2008 at 9:19 PM, Harry Halpin <hhalpin@ibiblio.org> wrote:
> Richard H. McCullough wrote:
>> I'm first trying to understand the definitions of "Class" and "Thing"
>> in RDF/OWL.
>> In the past, I have suggested different definitions, which I would have
>> used in mKR.  But I only did that because I couldn't understand the
>> RDF/OWL definitions.  I'm still trying to understand.
>> I'm looking for help, for clarity.
>> I think these questions are appropriate topics for the Semantic Web.
>> If these questions can not be answered, then your "Semantic" Web
>> is manipulating meaningless symbols.
> They are appropriate assuming you have looked at the specs and are asking a
> reasonable question, not "Hey, I happen to have my own idiosyncratic way of
> using these words, why doesn't the SemWeb agree, and by the way, I haven't
> looked at the specs."
> Here's the specs. Note that OWL is not doing metaphysics per se, but it's a
> knowledge representation language that like every KR language, including
> supposedly "perfect" ones, makes some design choices. You may not agree with
> them, that's fine, you can use another one or create your own (which you
> seem to have done).
> However, I think the spec writers were reasonably and admirably clear,
> providing both an English definition and a formal one (that's about as clear
> as you get once you get your head around the formalism). While their
> definitions may be different than your 'common-sense' ones, remember that
> people have radically different intuitions about the meaning of 'thing'
> metaphysically. I for one endorse the stance of Alfred Whitehead, while you
> like Ayn Rand. That's fine - the SemWeb OWL WG made its own choices here,
> and one should not, read any "magic" - much less "metaphyiscal assumptions"
>  into the mnemonics used by OWL just because certain English words were used
> in their URIs. Remember URI Opacity!
> So, back to the specs:
> English Language Definition of OWL Class:
> "Classes provide an abstraction mechanism for grouping resources with
> similar characteristics. Like RDF classes, every OWL class is associated
> with a set of individuals, called the /class extension/. The individuals in
> the class extension are called the /instances/ of the class. A class has an
> intensional meaning (the underlying concept) which is related but not equal
> to its class extension. Thus, two classes may have the same class extension,
> but still be different classes."[1]
> English Language Definition of owl:Thing:
> You should probably read: "Two OWL class identifiers are predefined, namely
> the classes  owl:Thing and  owl:Nothing. The class extension of owl:Thing is
> the set of all individuals. The class extension of owl:Nothing is the empty
> set. Consequently, every OWL class is a subclass of owl:Thing and
> owl:Nothing is a subclass of every class" [2]
> I think the problem you are encountering is that owl:Thing is used to
> introduce individuals often, since all individuals are a subclass of
> owl:Thing, one by default if one wishes to say very little about a new
> individual one can simply state it's a member of the class of owl:Thing,
> since *every* individual belongs to owl:Thing (except owl:Nothing and in
> OWL-DL, datatyped literals). If one wishes to say more, one can use a new
> class, which identifies a subset of owl:Thing and so is a sub-class of
> owl:Thing.
> Formal Definition of owl:Thing
> Note that since OWL-DL tends to divide resources into individuals (ABox) and
> classes (TBox) and RDF allows these resources to be mixed up, there's two
> formal definitions, one for OWL DL/Lite and another compatible with RDF.
> OWL:
> http://www.w3.org/TR/owl-semantics/direct.html#owl_Class_semantics
> RDF:
> http://www.w3.org/TR/owl-semantics/rdfs.html#owl_Class_rdf
> OWL:
> http://www.w3.org/TR/owl-semantics/direct.html#owl_Thing_semantics
> RDF:
> http://www.w3.org/TR/owl-semantics/rdfs.html#owl_Thing_rdf
> If you find this all indecipherable, I believe Hendler and others have put
> out pretty good books on the subject you may find of interest. Unforunately
> there isn't yet a good text I have found on "How to Read Formal Semantics"
> but maybe someone else on the list has recommendations.
> I am afraid I won't have time to answer any more hopefully reasonable
> questions on this matter, but maybe some of the OWL experts on the list can
> help with any more questions. I'd phrase the questions in OWL though, rather
> than a custom KR language that others probably aren't familiar with or don't
> use. If examples are in MKE or whatever, please keep that *off* SemWeb
> lists, as it's isn't part of the SemWeb and  trust me, if you think you are
> having a hard time understanding the SemWeb, most people have on the SemWeb
> list can't make heads or tails of an MKE example.
> [1] http://www.w3.org/TR/owl-ref/#Class
> [2] http://www.w3.org/TR/owl-ref/#ClassDescription
>> Dick McCullough
>> Ayn Rand do speak od mKR done;
>> mKE do enhance od Real Intelligence done;
>> knowledge := man do identify od existent done;
>> knowledge haspart proposition list;
>> http://mKRmKE.org/
>> ----- Original Message ----- From: "Harry Halpin" <hhalpin@ibiblio.org>
>> To: "Richard H. McCullough" <rhm@pioneerca.com>
>> Cc: "Jack Krupansky" <jack@basetechnology.com>; "Semantic Web at W3C"
>> <semantic-web@w3.org>
>> Sent: Wednesday, August 27, 2008 5:01 PM
>> Subject: Re: Thing and Class
>>> While I'm sure we all appreciate the work done on MKR, could we keep
>>> MKR-specific posts to a MKR-list, not a Semantic Web list. While Richard
>>> (Dick) McCullough is free to develop any interpretation of "class" and
>>> "thing" he wants in MKR, of course, but the Semantic Web community uses the
>>> ones in the W3C Specs, and I thought they were clear in the specs. If MKR
>>> disagrees, that's fine (there's a long tradition of disagreeing about rather
>>> vague high-level concepts like 'class' and 'thing'), but that's not a
>>> question about the  Semantic Web.
>>> Richard H. McCullough wrote:
>>>> I want to banish Class to the bookkeeping context, where it belongs.
>>>> When two classes are equivalent, it means they have the same members,
>>>> but different definitions -- which means they are in different contexts.
>>>> When you merge the two contexts together, you get confusion.
>>>> Which class are we talking about now -- Class or Thing?
>>>> Which definition are we talking about now -- Class or Thing?
>>>> The class "cup" abstracts all properties of its individual member
>>>> "cups".
>>>> That includes how a cup is used, what a cup is made of, etc.
>>>>   cup subClassOf Thing;
>>>> includes all those properties.  We might call this cup-the-Thing
>>>> But when you say
>>>>   cup type Class;
>>>> you're in a different context - talking about cup-the-Class.
>>>> That's what I refer to as the bookkeeping context.
>>>> If you insist on dragging Class into the Thing context,
>>>> then I recommend doing it in the form of a ClassSet.
>>>>   cup ismem ClassSet;
>>>>   ClassSet type Set;
>>>>   Set  subClassOf  Thing;
>>>> Dick McCullough
>>>> Ayn Rand do speak od mKR done;
>>>> mKE do enhance od Real Intelligence done;
>>>> knowledge := man do identify od existent done;
>>>> knowledge haspart proposition list;
>>>> http://mKRmKE.org/
>>>> ----- Original Message ----- From: "Jack Krupansky"
>>>> <jack@basetechnology.com>
>>>> To: "Richard H. McCullough" <rhm@pioneerca.com>
>>>> Sent: Wednesday, August 27, 2008 2:49 PM
>>>> Subject: Re: Thing and Class
>>>>> But... if you get rid of Class, doesn't it then follow that subClass is
>>>>> no longer defined or of comparable meaning?
>>>>> Is there a subThing that is "class-like"? I would imagine that subThing
>>>>> is a decomposition of a Thing into the subThing's of which it is composed,
>>>>> which is not "class-like" categorization, although it has some reductionist
>>>>> appeal. But, a purely reductionist analysis does not look outwards to levels
>>>>> of abstraction for how a Thing is externally viewed, perceived, and used.
>>>>> Two "cups" would not have Class "cup" that recognizes an abstraction about
>>>>> how a cup is used, but would be classified as to their material and form of
>>>>> construction as Thing's.
>>>>> -- Jack Krupansky
>>>>> ----- Original Message ----- From: "Richard H. McCullough"
>>>>> <rhm@pioneerca.com>
>>>>> To: "Semantic Web at W3C" <semantic-web@w3.org>; "KR-language"
>>>>> <KR-language@YahooGroups.com>; "cyclify austin"
>>>>> <cyclify-austin@yahoogroups.com>
>>>>> Sent: Wednesday, August 27, 2008 4:59 PM
>>>>> Subject: Thing and Class
>>>>>> Since  Thing  subClassOf  Class;
>>>>>> and     Class  subClassOf  Thing;
>>>>>> it follows that  Thing  equivalentClass  Class;
>>>>>> So, I say:  get rid of Class!
>>>>>> Dick McCullough
>>>>>> Ayn Rand do speak od mKR done;
>>>>>> mKE do enhance od Real Intelligence done;
>>>>>> knowledge := man do identify od existent done;
>>>>>> knowledge haspart proposition list;
>>>>>> http://mKRmKE.org/
Received on Thursday, 28 August 2008 01:30:27 UTC

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