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Re: Ontology evolution

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Mon, 18 Mar 2002 16:57:32 -0500
Message-ID: <3C9662CC.57E7F21F@cse.lehigh.edu>
To: Hal Noyes <hnoyes@mindspring.com>
CC: public-webont-comments@w3.org
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

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
Received on Monday, 18 March 2002 16:57:35 GMT

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