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Re: SEM: Light review of semantics document

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 8 Nov 2002 10:34:24 -0600
Message-Id: <p05111b1cb9f1820f11c6@[65.217.30.130]>
To: Jim Hendler <hendler@cs.umd.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.

Well, sure, but apparently what you and Jeff meant by 'ontology' 
wasn't what I meant. Thats the trouble with English, right? Which is 
one reason why we are doing all this in the first place...

><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.

I have no problem with that, but I have always understood this to 
simply be an XML marker for the presence of OWL syntax in the RDF 
graph. Why do we need to say anything more than that? "owl:ontology" 
isn't in the graph, right? So its not in the namespace, and it has no 
semantics. If "owl:ontology" is in the OWL namespace, then we ought 
to say what an RDF triple which includes that name means.

>The issue we need to address is that IN ENGLISH USAGE (not formal logic)

I do wish you would make at least an effort to disguise your built-in 
anti-logical knee-jerk, Jim. It just gets in the damn way. What we 
are all doing here, whether you like it or not, is using ENGLISH to 
talk ABOUT a FORMAL logical language. When using ENGLISH it is often 
a good idea to use words which refer to concepts that actually make 
some sense in the context being talked about.

>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).

The difference is that one of them contains OWL syntax and the other 
does not. End of story.

What about the many other cases, such as  <rdf:RDF>....</rdf:RDF> 
which contains non-ground RDFS, say? What about one of those that 
contains RDFS which would break fast-OWL? What do we call those?  If 
some RDF uses rdf:bag, is it instance data? What about an rdf:List, 
described using bnodes? You (and Jeff) are confusing two different 
distinctions: ground versus non-ground, and RDF vs OWL. That is a 
dangerous confusion to incorporate into an official terminology.

>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

I'm tempted to respond that anyone who you would classify as a 
non-logician is already confused in any case. But I won't.

>-- 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.

Sorry, I object to this, because it doesn't make sense. You are 
presuming something that is false: that RDF can only be used to 
describe ground facts. We ought to use a naming convention that warns 
the world not to get this confused, rather than casting the confusion 
in stone.

I know that RDF is often used for instance data, but it can be used 
for other things. I frequently meet people in the DAML community who 
are surprised to hear that RDF allows bnodes; there is deployed 
software with serious bugs arising from the misunderstanding that RDF 
is used only for ground facts.  Also, this convention makes nonsense 
of the fundamental presumption that one can merge RDF graphs. If 
OWL/RDF really is RDF then this terminological usage becomes 
nonsensical even when applied to actual documents. It already doesn't 
make any semantic or operational sense.

Pat

>
>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
>>>>
>>>>  --
>>>>  ---------------------------------------------------------------------
>>>>  IHMC                                    (850)434 8903   home
>>>>  40 South Alcaniz St.                    (850)202 4416   office
>>>>  Pensacola                               (850)202 4440   fax
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>>>>  phayes@ai.uwf.edu                 http://www.coginst.uwf.edu/~phayes
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>>
>>
>>--
>>---------------------------------------------------------------------
>>IHMC					(850)434 8903   home
>>40 South Alcaniz St.			(850)202 4416   office
>>Pensacola            			(850)202 4440   fax
>>FL 32501         				(850)291 0667    cell
>>phayes@ai.uwf.edu	          http://www.coginst.uwf.edu/~phayes
>>s.pam@ai.uwf.edu   for spam
>
>
>--
>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


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40 South Alcaniz St.			(850)202 4416   office
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Received on Friday, 8 November 2002 11:34:05 GMT

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