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Fwd: Re: LANG: owl:import - Two Proposals

From: Jim Hendler <hendler@cs.umd.edu>
Date: Wed, 2 Oct 2002 12:50:46 -0400
Message-Id: <p05111707b9c0d45aff75@[192.168.0.24]>
To: webont <www-webont-wg@w3.org>

This one also

>Sender: heflin@EECS.Lehigh.EDU
>Date: Wed, 02 Oct 2002 12:07:36 -0400
>From: Jeff Heflin <heflin@cse.lehigh.edu>
>Organization: Lehigh University
>X-Accept-Language: en
>To: Jim Hendler <hendler@cs.umd.edu>
>Subject: Re: LANG: owl:import - Two Proposals
>
>Jim,
>
>Here's another one I think you sent only to me. If you meant to send it
>to  the mailing list, please do so and I will respond there.
>
>Jeff
>
>Jim Hendler wrote:
>>
>>  Elsewhere Jeff asked if those who prefer proposal 1 could address the
>>  disadvantages of 2 - here's that addressing
>>
>>  >
>>  >
>>  >Proposal #2
>>  >-----------
>>  >Syntax:
>>  >The imports syntax is in the domain of discourse of RDF, but not OWL.
>>  >Essentially we have a class called owl:Ontology and a property
>>  >owl:imports which can hold between a pair of Resources. Statements
>>  >are made about the current document using an empty URI reference
>>  >(this assumes that this expands to the current URI context).
>>  >The meaning of any statements which include
>>  >owl:imports as a subject or object is undefined. Syntactically, this
>>  >approach is the same as that of DAML+OIL. For example:
>>
>>  >[snip]
>>
>>  >
>>  >(where merge is as defined in the draft RDF model theory [1]).
>>  >
>>  >Pros:
>>  >- It is possible to query an RDF graph to obtain information about
>>  >what resources are ontologies and which ontologies import others.
>>  >
>>  >Cons:
>>  >- Having valid syntax that has undefined semantics may lead to reduced
>>  >interoperability. In particular, some users may build ontologies that
>>  >rely on the arbitrary decisions made by their favorite tool vendors.
>>
>>  yes - but all langauges have some of these undefined, and we already
>>  have them in our language unless we go to the strong model Peter
>>  proposes in which case it is not an OWL document unless a particular
>>  schema validates it -- As I've said often, my opinion is that that is
>>  unworkable in the wild.  I don't see where there is a problem to say
>>  it is undefined to  doing something that is unlikely to be done
>>  anyway (i.e. subclassing owl:ontology info or changing it's rdf:type)
>>
>>  but, if some user community finds a reason to do this, implements it,
>>  and a bunch of people find it useful - then it means the "Owl 2.0" WG
>>  should look at it -- that's how web languages evolve, and I think it
>>  is tremendous hubris on the part of our group to think we'll get it
>>  "right" the first time.
>>
>>  >
>>  >- It is unclear what it should mean if a document C contains the
>>  >statement A owl:imports B. Should this be another undefined construct?
>>  >If so, how can you determine from a graph if the subject of an imports
>>  >statement is the URI of the document from which the imports statement
>>  >comes?
>>
>>  I don't understand this.  We would have a graph which includes the
>>  statement in the graph that
>>
>>  :thisDocument owl:importants foo:thatDocument.
>>
>>  this would be useful for people who want to handle name space
>>  extractions and the like.  But rather than arguing this at length,
>>  let me say that the alternative -- imports not appearing in the graph
>>  -- certainly provides LESS information than having it.
>>
>>  >- The fact that an ontology's classes and properties do not occur
>>  >between the <Ontology> tags is unintuitive
>>
>>  I don't disagree with this - but again would ask about instance data.
>>  I strongly resist having instances HAVE to be in an ontology context
>>  (because they may be created by tools that are not OWL aware or are
>>  hand generated - i.e. we create a lot now using the tool "emacs"
>>  which is a great OWL instance creator (esp. using the DAML mode).
>>
>>  >
>>  >- The use of about="" to make statements about the enclosing document
>>  >seems like a hack. In particular is seems like we could be confusing the
>>  >notion of a document that describes an ontology and the concept of an
>>  >ontology itself.
>>
>>  I agree, but the problem is the only alternative you offer is to make
>>  the notion of the document and the ontology be indistinguishable,
>  > which to me defeats a lot of what I think the SW is all about.  I
>>  would rather see us actually define what an ontology is (see my
>>  earlier message in the previous thread about having an explicit
>>  ontology statemtn with a list of the URIs it contains) which would be
>>  a far more elegant solution to this particular problem which would be
>>  better than either of the two proposed solutions here -- it didn't
>>  get enough traction in the WG to be reintroduced here - my point
>>  being we've already rejected an approach that would solve this
>>  problem better than proposal 1 does, leading me to believe the WG
>>  doesn't see this as the critical issue.
>>
>>  >- The approach only partially succeeds in its goals, because although it
>>  >represents ontologies and their properties, it loses the ability to
>>  >recognize the boundaries of an ontology (i.e., what it contains) as soon
>>  >as two or more graphs are merged together. In particular, if this
>>  >approach is extended for use with versioning, then we lose the ability
>>  >to know which statements come from which version of an ontology.
>>  >
>>
>>  I agree, but again if this is what we want critically, we have
>>  seevral good non-document ways of doing it, which the WG hasn't
>>  seemed excited by.
>>  >
>>  >Recommendation:
>>  >---------------
>>  >Given the pros and cons of each proposal, I have a strong preference for
>>  >proposal #1, but could live with proposal #2 if the WG was certain that
>>  >its benefits outweighs its numerous costs.
>>
>>  I'm convinced for 2, not for 1 - so I'd love to see some other
>>  members of the WG get involved in the discussion...
>>
>>  --
>>  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


-- 
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 Wednesday, 2 October 2002 12:51:38 GMT

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