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Re: A perspective on ontology versioning

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Mon, 23 Sep 2002 15:08:11 -0400
Message-ID: <3D8F669B.D4F76E84@cse.lehigh.edu>
To: Christopher Welty <welty@us.ibm.com>
CC: www-webont-wg@w3.org


Thanks for the message. I think it does a good job of stating the pros
and cons of adding ontology versioning to OWL. I have gone through much
of these arguments with myself, and think that my current proposal is a
good intermediate solution. You are right that there are a lot of
complex issues that are more research oriented, and we shouldn't hastily
jump into those. My proposal is, as you say, basically "comments," with
the exception of some minor semantics for backward-compatibility, which
makes a certain amount of interoperability easier for ontology author to
specify. I thinking making backward compatibility just a comment too
would limit the scalability (over time) of our language, as I mentioned
in my use case.

Hopefully, your well-expressed comments will prompt others to discuss
their feelings on this matter.


Christopher Welty wrote:
> To paraphrase Jim:  In the past several years I've been building
> ontologies and doing research in the general area of ontology and one of
> the top ten, probably top five, issues that has emerged is versioning.
> Regarding how to deal with it in OWL, I find myself on the fence.  I want
> to stress that this is not because I don't care, in fact I care quite a
> bit, but I just don't know at this stage what a good course of action
> would be.  Here are a few notes from my perspective, in case someone is
> interested.   It's constructed as an almost desultory argument with
> myself, but I think it is a fair summary of both sides of the issue:
> - Ontology versioning is a very important issue in real world ontology
> use.
> - As Ian has often said of other things, however, it is a current research
> issue and I am a bit reluctant to see us make a committment to something
> that isn't well understood in the research community.
> - Still, it would be disappointing if we couldn't do something more than
> simply "a comment" (as Jim proposed), even if that comment is of some
> standard form that we claim we will look at later.  It seems to me the
> capability to make comments exists without OWL.  If this is one of the top
> ten questions asked about OWL, then it seems to me this answer would not
> be very satisfying to those grappling with the problem today.
> - But of course, in software, versioning is almost never part of the
> language used to specify the software.  CVS, SCCS, RCS, etc., (kinds of
> version control software) all use extra-language documentation (comments)
> or filesystem features to do fairly course-grained versioning.  It is only
> "by contract" that one version of software component is consistent with
> another (where "by contract" I mean that the author of the software simply
> declares it so).  Such systems, given a standard version tag, could easily
> be made to work with ontology artifacts when viewed as files.
> - However, while the issues of ontology versioning are seductively similar
> to those of software versioning,  there are some subtle points where they
> can be differentiated.  If an ontology is taken to be a declarative
> logical and/or deductive specification of meaning (which I note software
> is NOT), then there should be ways in which more information about
> versions can be specified declaratively and provably, FAR easier than with
> software.  Furthermore, if the role of an ontology language is to support
> computational means to enforce and deduce the consequences of the
> specifications, then it also makes sense that a specification of versions
> should fit into a computational framework.
> - Nevertheless, ontology versioning is extremely complex, since it
> requires a very difficult distinction between the syntax and the semantics
> of the ontology artifact - what is being versioned, the real-world classes
> and relations the ontology talks about, or the individual statements (or
> collections of them) in the language being used?  How are these
> "versionable units" circumscribed?
> - There does seem to be a higher level, more course-grained and tractable
> view, which is basically that proposed by Jeff: treat "Owl:ontology"s as
> versionable artifacts of which you can state one basic provable thing:
> that one version is logically consistent with another.  This seems like a
> fairly useful thing to say, especially if you take the more traditional
> view that an ontology does not generally contain instances (with a few
> exceptions), but merely specifies the classes and relations available to
> describe instances.  Having a consistency guarantee between versions means
> that any data that "worked" with the previous version of the ontology will
> "work" with the new one.
> - This is far more difficult than it sounds, however, because the
> association between statements in the new ontology version and statements
> in the old version will not be easy to align.  As a practical matter, it
> seems quite hard, and it doesn't seem as if you'd be gaining anything more
> than you would by simply importing the old version, and stating just the
> monotonic additions in the new version.
> - That view unfortunately ignores another practical matter: ontologies,
> even small ones, that are spread out and fragmented as, in this case, a
> chain of imports, are extremely difficult to manage.   There are huge
> maintainability arguments for keeping large chunks together.  Much of this
> could be addressed by tools, but not all.
> - This also ignores "prior-version" and "deprecates" since they seem to be
> basically comments (ie their meaning is outside the language).
> Finally, much of what I'm saying here is based on my own belief that the
> purpose for an ontology language like OWL is to go beyond "meaning by
> contract".  We already have technology that allows one person to say,
> "this is what I mean by X".  Ontology languages shoudl allow us to more
> precisely define the meaning of terms and then automatically and more
> reliably explore the logical consequences of what we say.
> -Chris
> PS I wrote this message rather hastily, so if anything seems disparaging
> it was not intended as such.
> Dr. Christopher A. Welty, Knowledge Structures Group
> IBM Watson Research Center, 19 Skyline Dr.
> Hawthorne, NY  10532     USA
> Voice: +1 914.784.7055,  IBM T/L: 863.7055
> Fax: +1 914.784.6078, Email: welty@us.ibm.com
Received on Monday, 23 September 2002 15:08:14 UTC

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