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Re: Thing and Class

From: Richard H. McCullough <rhm@pioneerca.com>
Date: Wed, 27 Aug 2008 21:55:23 -0700
Message-ID: <16C5C32A02B741A584068A0BDC865B61@rhm8200>
To: "Harry Halpin" <hhalpin@ibiblio.org>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>

Jack
I removed your dangling Cc: line

Harry
I have read the RDF and OWL specs,
but as Tim Berners-Lee pointed out,
I haven't remembered them all correctly.

Thank you for your clarifications below.
I've skimmed them, but I want to read
them again very carefully.

I have also thought of a good way to focus on my concerns.
I will take a simple example, maybe the one offered by
James Leigh, and do a complete individual hierarchy
using all "type" and "subClassOf" links -- according to
RDF/OWL, not according to mKR.

I hope you won't mind if I use a notation similar to mKR
to distinguish between "type" and "subClassOf" links.
I plan to show
    x  type  y
as (that's an "i:" prefix)
y
/  i:x
and
    x  subClassOf  y
as
y
/  x

I'll have the example done tomorrow.

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 6:19 PM
Subject: Re: Thing and Class


> 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 05:02:24 GMT

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