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Re: Ambiguity of "RDF namespace" - was: Re: Contradicting definitions of "property"

From: Richard Cyganiak <richard@cyganiak.de>
Date: Wed, 9 May 2012 21:49:29 +0100
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-Id: <D41182CF-0086-4F1E-B4FF-B82DE4C32E4F@cyganiak.de>
To: Thomas Baker <tom@tombaker.org>
On 9 May 2012, at 16:01, Thomas Baker wrote:
>>>> Namespace: A set of IRIs that syntactically start with the same sub-IRI.
>> 
>> To pick an analogy with natural language: ?Alice, Bob, Charlie? is a
>> ?vocabulary? (assuming the names have clearly established referents in your
>> universe). ?All sequences of letters starting with A? is a ?namespace?. Most
>> of the sequences in the namespace don't mean anything (they don't have
>> referents), but that's not required for being a member of a namespace.
> 
> I accept the analogy, but I'm unsure what you mean by "most of the sequences in
> the namespace" not having referents.  If you mean "potential sequences" then of
> course that is true.  But "namespace," as I see it being used, implies a set of
> IRIs explicitly "declared" by the namespace's "owner."  

Well, that's not the way I see it. I understand a namespace as the set of *all* IRIs starting with the namespace IRI.

How about this other approach? There's no such thing as a “namespace” in RDF. Just avoid the term on its own — it's a remnant of the old XML baggage. Some of the other related XML terms that came along with it have proven to be useful though: Some RDF syntaxes offer a way of associating “namespace prefixes” with “namespace IRIs” in order to abbreviate IRIs; and there's “namespace documents” which describe the terms in an RDF vocabulary all of whose terms start with the same IRI. The term “namespace” on its own is just a sloppy way of referring either to such an RDF vocabulary or to a namespace IRI.

>>> Also, the current draft of RDF Concepts 1.1 [1] still says:
>>> 
>>>   "Vocabulary terms in the rdf: namespace are listed and described in
>>>   detail..."
>>> 
>>>   This suggests that the "rdf: namespace" holds not just any IRIs, but
>>>   "vocabulary terms" denoted by IRIs.  
>> 
>> That's not a valid inference. It says that *some* of the things in the rdf:
>> namespace are vocabulary terms. It doesn't say that all of the things in the
>> rdf: namespace are vocabulary terms.
> 
> Strictly speaking, I do not think the sentence says that _all_ of the things
> in the rdf: namespace are vocabulary terms.  But it also does not say that all of 
> the vocabulary terms in the rdf: namespace are listed and described in detail.

Not sure what your point is.

> It is not incorrect, then, to use the same IRI both as a namespace IRI
> and to denote a vocabulary?

It's not incorrect and it is fairly common practice AFAICT.

>> [[
>> An OWL ontology is a formal description of a domain of interest, and can be
>> used to describe the terms in an RDF vocabulary and their relationships. OWL
>> ontologies can themselves be expressed as RDF graphs, using terms in the owl:
>> namespace. OWL is more expressive, but also more complex, than RDF Schema. In
>> fact, OWL contains RDF Schema as a simple subset.
>> ]]
> 
> Fine, but that's an OWL ontology.
> 
> What about "ontology"?  

I won't go anywhere near that question.

> Does "ontology" mean "OWL ontology"?  

I suppose every OWL ontology is an ontology? But obviously there are other kinds of ontologies, and there's ontology as a branch of philosophy.

> Is [1] an ontology?  

It's a (manifestation of an) OWL ontology. Every OWL ontology is an ontology. Therefore, [1] is an ontology.

> Does its use of "owl:equivalentProperty" make it an "OWL" ontology?  

It doesn't need to use any OWL vocabulary to be an OWL ontology. As I said: “OWL contains RDF Schema as a simple subset.”

(Strictly speaking, an RDF document doesn't even need to define any classes or properties to be an OWL ontology. *Any* RDF document is a (degenerate) OWL document. But that's just sort of an accident in the way OWL is defined.)

Best,
Richard



> I'd just like to flag this...
> 
> [1] http://dublincore.org/2010/10/11/dcterms.rdf#  
> 
>>> Is it really a document I can print out and staple to the wall?
>> 
>> Well, the first step to unraveling this would be an excursion into the
>> Work/Expression/Manifestation/Item distinctions of FRBR. I'd say, an ontology
>> is a kind of Work. The ontology formalized in OWL 2 and written in RDF/XML
>> syntax is an Expression or maybe a Manifestation of that Work. My printout is
>> an Item of the Work.
> 
> Yes indeed - now we're talking...!
> 
> Tom
> 
> -- 
> Tom Baker <tom@tombaker.org>
> 
Received on Wednesday, 9 May 2012 20:50:00 GMT

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