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Re: Multi-layered Knowledge Representations for Healthcare (was RE: An argument for bridging information models and ontologies at the syntactic level)

From: Dan Russler <dan.russler@oracle.com>
Date: Thu, 24 Jul 2008 15:41:35 -0400
Message-ID: <4888DAEF.7000203@oracle.com>
To: Samson Tu <swt@stanford.edu>
CC: "Kashyap, Vipul" <VKASHYAP1@PARTNERS.ORG>, "Elkin, Peter L., M.D." <Elkin.Peter@mayo.edu>, public-semweb-lifesci@w3.org, public-hcls-coi@w3.org
Hi Samson,

If "denote" = "describe" in your sentence, then I withdraw my objection.

My concern is that the term "class" as used in UML doesn't seem to mean 
the same thing as you are describing for a class in OWL. For instance, I 
don't see the same concept of "resource" in the definition of class in UML.

A UML static diagram is just a symbolic method of displaying a set of 
related assertions, i.e. attribute assertions, association assertions, 
and state transition (behavior) assertions. The semantic interpretation 
of what the class means comes not only from the text definition of the 
"class symbol," but also from inferences made from the entire network of 
attributes, associations, and state transitions.

To infer from a UML class more than is implied by the the above 
statement is incorrect.

If we can agree on that, then we can better evaluate the equivalent and 
non-equivalent semantics of OWL and the other methods for organizing 
sets of assertions.


Samson Tu wrote:

> Dan Russler wrote:
>> Hi Samson,
>> We are getting closer.
>> 1) In the reference you site..."A class is the descriptor for a set"...
>> 2) Earlier, you stated that "semantics of a class as denoting a set 
>> of instances."
>> I believe these two statements represent the "apples" and "oranges" 
>> you referenced:
>> Statement 1) is the traditional "a class describes the attributes and 
>> associations for a concept that are common to a set of instances."
>> Statement 2) is better described by your population example.
>> I wasn't objecting to 1) . I was objecting to your seeming to 
>> confusie the 2) with 1).
>> However, if you claim that "denote" means the same thing as 
>> "describe," then I would agree with you instead of objecting to your 
>> assertion.
>> To be a little clearer....The definitions in a set of dictionaries 
>> all "describe" the meaning of the word "farmer." However, the word 
>> "farmer" in a dictionary does not "denote" the set of instances of 
>> farmers in the world. Same with a UML class titled "farmer."
> Dan,
> Yes, I am claiming that "denote" means the same thing as "describe" in 
> my intended usage of the English words.
> We are talking about the semantics of "class." The class "farmer" is 
> not the same thing as the dictionary word "farmer." Some people say 
> that UML is just a graphical notation without semantics because it 
> does try to make its meaning of the word "class" very clear. In 
> logic-based knowledge representation languages, the set-theoretic 
> semantics of class is widely used.
> The OWL Reference[1] put it this way:
> 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.
> OKBC [2] p. 6 put it even more baldly:
> A class is a set of entities. Each of the entities in a class is said 
> to be an instance of the class.
> In logical term, a class is a unary predicate satisfied by all of its 
> instances. Dictionary definitions of words are not involved.
> [1] http://www.w3.org/TR/owl-ref/#Class
> [2] http://www.ai.sri.com/~okbc/okbc-2-0-3.pdf
>Samson Tu                                   email: swt@stanford.edu 
>Senior Research Scientist                   web: www.stanford.edu/~swt/
>Center for Biomedical Informatics Research  phone: 1-650-725-3391
>Stanford University                         fax: 1-650-725-7944
Received on Thursday, 24 July 2008 19:43:04 UTC

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