Re: Ontology evolution

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 Monday, 18 March 2002 21:18:29 UTC