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jonathan@openhealth.org (Jonathan Borden) writes:
>1) There is nothing that prevents ontologies from changing fairly
>regularly. Ontologies themselves are just :-) documents,
>representations of resources :-) that can change as often as the
>author desires. Ontologies can be generated from databases etc. The
>only tricky point of this is designing systems that can deal with
>changing ontologies, but that is a software issue, not necessarily an
>ontology issue. In any case the WebOnt WG, which has a good number of
>people who have lots of experience with ontologies has considered
>these issues, indeed from the "use cases and requirements" document:
>http://www.w3.org/TR/webont-req/#goal-evolution . Note *requirements*
>R3 "explicit ontology extension" and R6 "versioning information" which
>are relevent to this issue.
Technically, ontologies can certainly change. Culturally, however, the
paeans to ontologies that I see appear driven by a deep need for a sense
of stability at least, a sense of monolithic truth at worst.
Economically, the whole thing is sold as "once you do this, you'll be
able to make all your information meaningful at low low cost", and I'm
not sure that's compatible with regular change.
>2) although the world is constantly changing, relationships need not
>so constantly change. For example, *you* and *your father* -- I don't
>need to know any details about you, nor about your father, and indeed
>both you and your father are constantly changing -- even for deceased
>people, for example, the "time since birth" is a property whose value
>is in a constant state of change. "physical location" is another
>property which might be in a constant state of change etc. etc.
>Nonetheless, the *relationship* <#Simon> :sonOf _:1 between the two of
>you need not change (I haven't even assigned a URI to your father!)
If all relationships changed all the time, we'd all be pretty confused.
The questions seem to arise around cases where changes in classification
possible, necessary, and often unpredictable.
>The point about this is that the constraints imposed by any ontology do
>not (typically) result in any single state of affairs, rather a *range
>of states of affairs*. A good ontology might capture a wide range of
>states while at the same time imposing the proper constraints on these
>states.
>
>Admittedly time dependent changes in the state of the world remains an
>area of current research for ontologies, OWL/RDF in specific, but
>while OWL may not have detailed specific mechanisms for dealing with
>time dependent state changes, the fact that such state changes might
>be important has been factored into and considered in the design of
>OWL itself i.e. future extensions to OWL might indeed directly capture
>time dependencies.
Great to hear, but I await experience on the matter. Versioning seems
to be a consistently hard problem - not because new versions are hard to
create, even annotate that they're new - but because change in one part
of a model generally has cascading effects through other parts of the
model and implementations based on the model.
>There is no reason that one should conclude that
>one has to throw out OWL, or move beyond OWL in order to model a
>changing world. Language itself is in a constant state of flux, yet
>Wordnet.
There are plenty of other reasons for throwing out such projects. None
of them seem particularly likely to win those suffused with ontological
fervor, though.
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