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Re: Ontology evolution

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Tue, 19 Mar 2002 10:52:45 -0500
Message-ID: <3C975ECD.3CE34A64@cse.lehigh.edu>
To: Jim Hendler <hendler@cs.umd.edu>
CC: Hal Noyes <hnoyes@mindspring.com>, public-webont-comments@w3.org
I agree that the language in the working draft is vague, and had
intended to keep this in mind for the next revision. I am sorry for not
mentioning this in my response to Hal.


Jim Hendler wrote:
> At 3:56 AM -0500 3/15/02, Hal Noyes wrote:
> >To the W3C Ontology Working Group -
> >
> >In section 3.2., Ontology evolution, of Requirements for a Web Ontology
> >Language, you state
> >
> >     "An important issue of revision is whether or not documents that commit
> >to one version of an ontology are compatible
> >      with those that commit to another. Both compatible and incompatible
> >revisions should be allowed, but it should be
> >     possible to distinguish between the two. Note that it is possible for a
> >revision to change the intended meaning of a term
> >     without changing its formal description.. Thus determining semantic
> >backwards-compatibility requires more than a
> >     simple comparison of term descriptions. As such, the ontology author
> >needs to be able to indicate such changes
> >     explicitly. "
> >
> >I don't get it. How can the meaning of a term within a universe of discourse
> >change, yet its formal description remain the same? Isn't that what
> >ontologies are for - to encode meaning? Unless you intend that "formal
> >description" simply refers to the human readable documentation comments
> >within the ontology, and not the encoded semantics of the term. If so, that
> >is not clear from the above. Please clarify.
> >
> >Thank you,
> >
> >Hal Noyes
> >Oracle DBA
> >Howard Systems International
> Jeff - I think Hal makes a good point - your explanation (below) is
> correct, but the wording in the report is somewhat ambiguous.  This
> might be a good place to tighten up the language and maybe to give an
> example -- in particular, the term "formal description" could imply
> underlying semantics rather than the syntactic OWL expression.
>   -JH
> At 4:57 PM -0500 3/18/02, Jeff Heflin wrote:
> >Hal,
> >
> >Thank you for your question. It is usually impossible to completely
> >formalize a domain. For example, consider how you would formalize the
> >definition of what it means to be a person. An ontology is simply an
> >approximation that consists of a set of axioms (definitions) that the
> >ontology author feels is "close enough" to his or her intended meaning.
> >If a change to the intended meaning is a subtle one, then the old formal
> >definition may still accomodate the new meaning. For example, consider
> >an ontology that said Employee was a subclassOf Person and did not
> >express any additional definitional information about the class
> >Employee. If the original intended meaning of this may class was
> >full-time employees, then a change to include consultants as members of
> >the class would not necessitate a change in its formal definition,
> >because it was loose enough to accomodate either meaning. In such cases,
> >the comment should indicate the intended meaning of the concept, in
> >order to help people use it correctly.
> >
> >Would it be better to create a new term and include additional formal
> >definitional information? Certainly, and the web ontology language will
> >support this. However, from an ontology author's point of view, this is
> >not always practical, particularly if mistakes were made in early
> >versions of an ontology. If you used a term incorrectly in an early
> >version of an ontology, should it be bound to that definition for all
> >time? I think not. Issues like this are the motivation for that ontology
> >evolution design goal.
> >
> >Jeff Heflin
> --
> 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)
> AV Williams Building, Univ of Maryland            College Park, MD 20742
> http://www.cs.umd.edu/users/hendler
Received on Tuesday, 19 March 2002 10:52:52 UTC

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