Re: namespace declarations and imports

Thanks for the clarification. I can see the difference now. My
misunderstanding was partly to do with an example I was following in a SW
book I'm reading that uses the FOAF ontology. In that example they create a
new ontology and declare the foaf namespace but never do an owl:imports, so
I mistakenly thought that their new ontology somehow had access to the foaf
ontology. What was actually happening was that in their Java code in Jena,
the foaf ontology is being read in and aligned with their own ontology.

Cheers,
Jim

On Wed, Jun 24, 2009 at 7:58 AM, Pat Hayes <phayes@ihmc.us> wrote:

>
> On Jun 23, 2009, at 6:18 PM, James Prentice wrote:
>
> I have a very newbie question I'm hoping someone can clarify. Say I'm
> creating an ontology and have several namespace declarations because I want
> to use some defined vocabularies, e.g. foaf:http://xmlns.com/foaf/0.1/ and
>
> owl:http://www.w3.org/2002/07/owl#. Maybe I want to use foaf:mbox and
> owl:sameAs.
>
> There are two issues here. You can use namespace declarations to help you
> write the URI references more compactly, but the actual ontology is using
> the full URI reference. (In NTriples notation this is made explicit, for
> example.) So you could write them all out in full and not use namespaces at
> all, and it would work exactly the same way. Then there is the question of
> whether using a URI creates any kind of link to another ontology. And the
> answer there is that it does not, though a lot of people (like yourself)
> feel that maybe it should. And maybe it often does in practice, etc. etc.
> BUt according to the specs, simply using a URIreference in an ontology does
> not automatically assert anything from its 'home' ontology, even if it has
> one. And its not obliged to have one. You control this stuff by importing
> (or not, as you choose.)
>
>  My question is, how are the foaf and owl definitions located?
>
>
> They aren't, unless you import them explicitly. And they aren't
> definitions, by the way, just more ontologies.
>
> Since URIs are not always resolvable, or may be resolvable to something
>
> other than the ontology itself, I'm wondering how they are loaded when I do
> something like run the Pellet reasoner on my ontology in Protege.
>
>
> They aren't. If you run a reasoner on your ontology, it runs on your
> ontology. If you include an imports, then your ontology includes the
> imported ontology, but if not, it doesn't.
>
>  Does it
> look up the URI in some common repositories and try to load from there?
>
> No.
>
>
> On a related note, I was confused by this paragraph from
> http://www.w3.org/TR/owl-ref/#imports-def
>
> "Although owl:imports and namespace declarations may appear redundant, they
>
> actually serve different purposes. Namespace declarations simply set up a
> shorthand for referring to identifiers. They do not implicitly include the
> meaning of documents located at the URI. On the other hand, owl:imports does
>
> not provide any shorthand notation for referring to the identifiers from the
> imported document. Therefore, it is common to have a corresponding namespace
> declaration for any ontology that is imported."
>
> Namespace declarations don't *only* set up shorthand, do they?
>
> Yes, that is all they do. Really.
>
>  If I declare
>
> the foaf namespace and then refer to foaf definitions in my ontology, at
> some point the foaf ontology has to be loaded.
>
> No, it doesn't. That is the point. You may be being misled by referring to
> foaf 'definitions'. OWL and RDF don't have definitions, just
> assertions (sentences, axioms, 'facts') There are no definitions that *
> have* to be loaded or used.
>
> I don't see a large
> difference between namespace declarations and imports.
>
>
> But you should.
>
> Pat Hayes
>
>
> I'm very confused by this issue, so it's possible that my question doesn't
>
> even make sense. :-) Thanks for any clarification of this issue.
>
> Cheers,
> Jim
>
>
> ------------------------------------------------------------
> IHMC                                     (850)434 8903 or (650)494 3973
> 40 South Alcaniz St.           (850)202 4416   office
> Pensacola                            (850)202 4440   fax
> FL 32502                              (850)291 0667   mobile
> phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
>
>
>
>
>