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Re: Why do you want to do that?

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 12 Aug 2008 09:44:40 -0700
Message-Id: <p06230928c4c76ab327e8@[]>
To: "Richard H. McCullough" <rhm@pioneerca.com>
Cc: "Frank Manola" <fmanola@acm.org>, "Adam Pease" <adampease@earthlink.net>, "Semantic Web at W3C" <semantic-web@w3.org>, "KR-language" <KR-language@YahooGroups.com>
At 5:01 AM -0700 8/12/08, Richard H. McCullough wrote:
>Hi Pat
>We've got a lot of confusion between us right now.
>I'll do my best to straighten it out.
>See below for my answers, comments, etc.
>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;
>----- Original Message -----
>From: "Pat Hayes" <<mailto:phayes@ihmc.us>phayes@ihmc.us>
>To: "Richard H. McCullough" <<mailto:rhm@pioneerca.com>rhm@pioneerca.com>
>Cc: "Frank Manola" <<mailto:fmanola@acm.org>fmanola@acm.org>; "Adam 
>Pease" <<mailto:adampease@earthlink.net>adampease@earthlink.net>; 
>"Semantic Web at W3C" 
><<mailto:semantic-web@w3.org>semantic-web@w3.org>; "KR-language" 
>Sent: Monday, August 11, 2008 11:15 PM
>Subject: Re: Why do you want to do that?
>  > At 10:56 PM -0700 8/11/08, Richard H. McCullough wrote:
>>>I finally got a few minutes to read OWL Guide 3.1.3
>>>I read that section as supporting my position.  The word "context"
>>>is mentioned
>>>several times, with the implication that X ismem IndividualSet; in
>>>one context,
>>>and X ismem ClassSet; in a different context.
>>  Is that actually asserted anywhere? Please give a citation.
>I said "implication".  It is not clearly asserted.  You have to read 
>between the lines.
>Here is the beginning of OWL Guide, section 3.1.3.
>Note the two fragments I have put in bold type.
>In the second one, the wording "could itself be considered" implies that they
>again mean "in certain contexts".

First, it means nothing of the sort. No contexts are mentioned. 
Second, this is only a tutorial guide. The actual specification 
documents of OWL/RDFS/RDF give precise semantics for these languages 
(actually for three versions of OWL, making a total of 5 distinct 
languages) which are normative rather than informative, so take 
precedence over anything that you conclude from reading between the 
lines of a tutorial introduction. And in RDFS and OWL-Full, classes 
are elements of other classes. In fact, in these languages there are 
classes which contain themselves as members, eg rdfs:Class does. And 
no mention of contexts anywhere.

>Note also that "could be considered" is not the same as "is".

True, but Frank was being ultra-careful not to offend the intuitions 
of beginners who might be puzzled by elementary set theory. As I say, 
this is an introductory tutorial document, not a specification. One 
should not draw too many conclusions from the subtleties of wording.

>To correlate with the mKR language, think "could be viewed".
>There are important issues regarding the distinction between a class 
>and an individual in OWL. A class is simply a name and collection of 
>properties that describe a set of individuals. Individuals are the 
>members of those sets. Thus classes should correspond to naturally 
>occurring sets of things in a domain of discourse, and individuals 
>should correspond to actual entities that can be grouped into these 
>In building ontologies, this distinction is frequently blurred in two ways:
>Levels of representation: It is well known that in certain contexts 
>something that is obviously a class can itself be considered an 
>instance of something else. For example, in the wine ontology we 
>have the notion of a Grape, which is intended to denote the set of 
>all grape varietals. CabernetSauvingonGrape is an example instance 
>of this class, as it denotes the actual grape varietal called 
>Cabernet Sauvignon. However, CabernetSauvignonGrape could itself be 
>considered a class, the set of all actual Cabernet Sauvignon grapes.
>Subclass vs. instance: It is very easy to confuse the instance-of 
>relationship with the subclass relationship. For example, it may 
>seem arbitrary to choose to make CabernetSauvignonGrape an 
>individual that is an instance of Grape, as opposed to a subclass of 
>Grape. This is not an arbitrary decision. The Grape class denotes 
>the set of all grape varietals, and therefore any subclass of Grape 
>should denote a subset of these varietals. Thus, 
>CabernetSauvignonGrape should be considered an instance of Grape, 
>and not a subclass. It does not describe a subset of Grape 
>varietals, it is a grape varietal.
>>>But a problem arises because OWL doesn't have contexts.
>>>So, apparently, the OWL solution to mix all contexts together,
>>>and ASSUME that all the propositions are still true.
>>  No. The OWL methodology, like that of virtually all modern logic, is
>>  to define a formal semantics for the notation, which then DETERMINES
>>  what is true and false. There are no assumptions anywhere. So there
>>  isn't a problem. And there are no contexts in OWL as it isn't a
>>  context-dependent language.
>The namespaces used (including rdf, rdfs, owl)
>contain propositions which are part of the context of
>every OWL "document".

If you like that way of speaking, I see what you mean; but it is 
misleading as there is only one "context" for each language.

>Every OWL "statement" has a context, which includes the "document" context.

No, it *is* the document context, as you have defined it above.

>In a list of OWL statements, each statement is part of the context of
>the OWL statements which follow it.

That is just technically wrong. OWL syntax is defined over RDF 
syntax, which is graph-based, so the order of statements in a 
document is irrelevant, and indeed might change when the document is 
transmitted. See the RDF Concepts paper for an introduction to graph 

>The mKR language explicitly says what the context is, using the format
>     at space=s, time=t, view=v { statement };

Yes, but that is a context *in mKR*, not a context in OWL. There are 
no contexts in OWL.

>>>To make this problem more apparent, we can specify the contexts
>>>     at view =  ind { X ismem IndividualSet; };
>>  What does that mean? What is the semantics of your formalism? Because
>>  if you were to provide one, that would stop all the argument, by
>>  answering the question.
>"ind" is the name of a proposition list, which is the context of the
>statement "X ismem IndividualSet;".

But that statement can appear in many different 'contexts', so the 
use of functional notation here is undefined.

>>>     at view = cls { X ismem ClassSet; };
>>>The question is: what happens when we mix the two contexts together?
>>  What DETERMINES what happens? How is consistency defined for your 
>>formal logic?
>Use all the propositions to deduce what is true, and what is false.

No, you misunderstand me. When you say 'use', you are presumably 
referring to some kind of inference. But what determines which 
inferences are valid, in your formalism? The usual way to do this is 
to have a semantics which determines truth in an interpretation. What 
is your way to do it?

If that is too hard, what inference rules do you have to perform 
deductions with?

>  >
>>>Pat Hayes says
>>>     at view = mix { X ismem IndividualSet; X ismem ClassSet; };
>>  No, I didn't say that, as I don't speak this language. I wrote in English.
>Agreed.  That is the mKR paraphrase of what you wrote in English.

But even in English, I did not refer to contexts or mixing of 
contexts. I simply said that it is consistent to say that something 
is both an individual and a class. Nothing there about contexts.


>>  Pat
>>>Dick McCullough says
>>>     at view = mix { not{X ismem IndividualSet;}; X ismem ClassSet; };
>>>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;
>>>----- Original Message ----- From: "Frank Manola" 
>>>To: "Richard H. McCullough" <<mailto:rhm@pioneerca.com>rhm@pioneerca.com>
>>>Sent: Friday, August 08, 2008 9:01 AM
>>>Subject: Re: Why do you want to do that?
>>>>On Aug 8, 2008, at 11:21 AM, Richard H. McCullough wrote:
>>>>>Over the last six years, I have suggested a number of
>>>>>"improvements" to the RDF language.  Not one of
>>>>>my suggestions was adopted.  Apparently,
>>>>>RDF is fine just the way is, thank you!
>>>>Yep.  That doesn't imply opposition to improvements though;  some
>>>>people think the way to provide the "improvements" they want is to
>>>>define languages "on top of" RDF (like the OWL dialects) rather
>  >>>than  making those changes directly in RDF.  That way, your
>>>>"improvement"  and my improvement can possibly co-exist more nicely
>>>>>I would now like to turn the tables, and ask
>>>>>why do you want to do that?
>>>>>I'll start with two features of RDF which seem to be popular.
>>>>>1. X  subClassOf  X;
>>>>>A neat mathematical property, right?
>>>>>But if you do the inferences, what it means is
>>>>>    X  sameAs  X;
>>>>>We already knew that.
>>>>>Why do you want to do that?
>>>>I need some help with this question.  Do you think being able to
>>>>say X subClassOf Y is OK?  If so, are you asking why RDFS (not RDF,
>>>>BTW) doesn't explicitly forbid the special case of X subClassOf X?
>>>>Why do  you want to do that (i.e., test for this special case all
>>>>the time)?   Or are you asking why people *write* X subClassOf X?
>>>>>2. X  type  Y;  X  subClassOf  Z;
>>>>>Another neat property: X is an individual and a class.
>>>>>Now I can ... What?  I don't know.
>>>>>Why do you want to do that?
>>>>How about the example in Section 3.1.3 of the OWL Guide?
>>  --
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Received on Tuesday, 12 August 2008 16:45:47 UTC

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