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Re: Defining subsets of existing OWL / RDF-S vocabularies in another vocabulary?

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Fri, 28 Sep 2007 19:14:18 +0100
Message-Id: <83E2DA11-6393-4B92-86CA-96C1A9E128DD@cs.man.ac.uk>
Cc: semantic-web-request@w3.org, semantic-web@w3.org
To: Matt Williams <matthew.williams@cancer.org.uk>

On 28 Sep 2007, at 18:50, Matt Williams wrote:

> Dear Bijan,
> I'd agree about the subclassing issue, but that doesn't seem to be  
> the same as redefining existing terms (if you subclass my term with  
> a new term, then wouldn't that mean I hadn't included it).

What if I add a constraint that makes your class a subclass of some  
existing class in your ontology. I.e., I add a subsumption.

> Nominals do blur the T/A line, but I still think it's a useful  
> distinction. The first defines what terms mean in relation to one  
> another; the second is a set if statements.

I don't think it's a bad distinction. I just don't think it supports  
a firm line between good changes to meaning and bad changes to  
meaning. Judgement is called for, always.

> Reusing terms and changing meaning ultimately means that you're not  
> reusing the semantic aspect of the term,

Yes. So?

> so reusing just the syntactic aspect seems odd;

Not at all. Say there's a ton of data marked up using your term. Now  
say I think you got the definition of the term wrong or I just want  
to explore alternative definitions. You're saying I should go back  
and change all the data?!

Nope. Not going to do it.

> if you want to keep the same terms, just change the NS (so all the  
> terms go from http://myOnt#someClass to http://yourOnt#someClass).

Why is this better? I mean, so you feel pure inside, I guess. But  
notice how it obscures the fact that you are *in fact* using the same  

Do I have to change my terms for *every update* I make to my  
ontology? Ewww.

> You're right that I could have made a mistake in defining things,  
> and you might see a quick fix....but then instead of reusing my  
> ontology, you should really use your own, even if that means  
> tweaking no more than the NS.

Why should really do so? What concrete benefit does it bring me.

> If you've seen an error, why not tell me about it?

Who said I didn't?

> The point about semantic "screwing" (perhaps need a better term!)  
> is that if I publish the ontology, you have the option to commit to  
> it, if you want to, as do others.

What if I just want to use it. I don't want to *commit*!

> My worry is not (so much) about merging ontologies as for systems  
> that use the ontologies: e.g. something that is looking for "All  
> men" or "all people with breast cancer" will have problems once you  
> start changing the meaning of the terms.

Isn't this swamped by all the other issues?

> I think for me it boils down the *point* of reusing ontologies; if  
> it's just for your own work, it doesn't matter, but if you're  
> aiming for interoperability, then you need to have shared  
> definitions, and so you need to not go around changing the  
> definitions of terms....

But if I munge all the terms in the data, then that data is now  
inaccessible to you! Isn't that worse? I'd rather deal with variant  
definitions of the same terms than lots of different terms each with  
their own definition.

Much rather.

Consider people who start by *collecting data*. They use terms but  
without a formal definition. Then many of us might take runs at  
trying to define those terms. We could do mappings and all that crud,  
but I really don't see a huge advantage. You do have to keep things  
straight, but you can do that in a number of ways (e.g., keeping  
track of the provenance of entailments). Renaming things is just one  
way to do that and not necessarily a great way, IMHO.

Received on Friday, 28 September 2007 18:13:03 UTC

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