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Re: SEM: Light review of semantics document

From: Jim Hendler <hendler@cs.umd.edu>
Date: Thu, 7 Nov 2002 18:36:48 -0500
Message-Id: <p0511170db9f0a726abcf@[128.8.127.214]>
To: pat hayes <phayes@ai.uwf.edu>, Jeff Heflin <heflin@cse.lehigh.edu>
Cc: www-webont-wg@w3.org

Sorry Pat, but I gotta agree with Jeff on this one- you signed onto 
this group which had "ontology" in the title, fully knowing by 
charter we would create something called an ontology language.

<owl:ontology>
   statements
</owl:ontology>

was in DAML+OIL, has been in OWL from day 1, a prereq for WG members 
was familiarity w/D+O, so you should have been aware that was there.

The issue we need to address is that IN ENGLISH USAGE (not formal 
logic) there is a need for us to say whether there is a difference 
between documents that look like

<rdf:RDF>

<owl:ontology ... />
...

<owl:class rdf:about="Moose">
   <owl:restriction>
     etc
   </owl:restriction>
</owl:class>

</rdf:RDF>

and documents that look like

<rdf:RDF>

<a:Moose rdf:id="MyMoose />

</rdf:RDF>

(and those which mix some of both).

Jeff's usage is consistent with the outside world's usage, and I 
suggest if we don't use it we will confuse everyone in the world 
except for logicians -- given that, I'd suggest we use it -- i.e.

Ontology documents are those that define classes and properties.
Instance documents are defined by using RDF to produce instances (or 
individuals) that are members of those classes with those properties.

OWL documents include each or documents which combine both.

I'm happy if someone wants a different term for "instance" documents.

I think the above is consistent with our current documentation.  I'm 
happy to see someone suggest rewording the above (Written quickly and 
not formally) in a way that is more technically correct -- but this 
is how most of the rest of the world will refer to what we have, so 
we should make it easy for them....
  -JH






  1:42 PM -0600 11/7/02, pat hayes wrote:
>>Pat, there is a terminology problem here. What you and Peter call
>>ontologies are different from what I call ontologies.
>
>Yeh, I had that impression. My problem is that I don't really know 
>what you are talking about.  I have never come across any useful 
>definition of "ontology" in our non-philosophical sense other than 
>something like "set of sentences" or maybe a document containing a a 
>set of sentences, etc.. If there is a real difference in your mind 
>between ontologies and other OWL thingies, then we ought to get this 
>clear and incorporate it into the language in some way.
>
>>My practical
>>definition is that OWL ontologies are only those OWL documents that
>>include the <owl:Ontology> tag.
>
>Hmm, I have to confess that I wasn't aware that 'owl:Ontology' was 
>in the OWL namespace. What is it supposed to mean?? Does it appear 
>in the RDF graph anywhere?
>
>But OK, an ontology is a *document*. In what language? I'm guessing 
>it has to be in  OWL/RDF/XML, right? So an OWL/RDF graph is not an 
>ontology(?)
>
>>All other OWL documents are not OWL
>>ontologies. Now, you are correct that a document with <owl:Ontology>
>>could consist of nothing but ground facts, and as such you don't
>>technically need to have a separate class of document for data. However,
>>the fact is, people only use the <Ontology> tag when they are defining
>>vocabularies (this statement is based on common usage in DAML). Are you
>>suggesting that these people should include <Ontology> tags is all of
>>their documents (see daml.org's list of data sets for a number of
>>examples of DAML documents without these tags)?
>
>I really don't give a rats about this tag, to tell you the truth, 
>but certainly people should somehow mark their OWL as being OWL; if 
>they don't, then they can't complain if an OWL engine misses it 
>entirely. We might want to follow RDF's lead and register an OWL 
>media type, though I think that idea is wrong-headed, myself. All I 
>care about is that we have some way to detect well-formed OWL which 
>is being asserted. Well-formed OWL means what it means as defined by 
>the OWL specs. The distinction between ground and non-ground OWL is 
>unimportant, seems to me, and there is no need to even refer to it. 
>If some piece of OWL has 10|6 ground facts and one non-ground fact, 
>I'm cool with that. What would you call it? Data with a dash of 
>ontology?
>
>>Or are you suggesting
>>that we should call these ontologies too?
>
>If we use the term at all, then yes, they are ontologies, in much 
>the same sense that a gazetteer is a book.
>
>>  I think the later would really
>>confuse users to call every document an ontology, but only some
>>ontologies are <Ontology> ontologies. In any case, all of our documents
>>need to be a lot more clear about terminology (e.g., which definition of
>>ontology does our WG use) and about how people should use ontologies to
>>describe real content.
>
>As to the last point, the distinction between ontology and data just 
>seems to make things more confusing, suggesting a distinction in 
>meaning that isn't there.
>
>Pat
>
>>
>>Jeff
>>
>>pat hayes wrote:
>>>
>>>  >pat hayes wrote:
>>>  >>
>>>  >>  >Here's some initial comments on the Semantics document dated Nov. 3:
>>>  >>  >
>>>  >>  >1) Sect. 2.2. The syntax needs the ability to represent documents that
>>>  >>  >consist soley of facts (that is, something other than ontologies).
>>>  >>
>>>  >>  ? Can you explain what you mean by "other than ontologies" ?Do you
>>>  >>  mean, not in OWL?
>>>  >>
>>>  >
>>>  >Part of this depends on what you consider OWL. From your response, I
>>>  >assume that you think of OWL as just a language for defining ontologies,
>>>  >and that you must use it with RDF in order to describe data
>>>
>>>  No. I fail to see the distinction you are drawing between 'ontology'
>>>  and 'data'. I don't know what you mean by this, or what importance it
>>>  has. One can have valid OWL documents which consist of nothing but
>>>  ground RDF facts. So?
>>>
>>>  >(e.g., a
>>>  >product catalog, a univeristy's course offerings, etc.). I tend to think
>>  > >of OWL as an extension to RDF, so this data is still part of OWL, it
>>>  >just has the standard RDF syntax.
>>>  >
>>>  >In any case, our model theory must talk about data to the same extent
>>>  >that it talks about ontologies.
>>>
>>>  It does. It always has done. What is the problem?
>>>
>>>  Pat
>>>
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>
>
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-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
Received on Thursday, 7 November 2002 18:36:55 GMT

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