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

From: Thomas Baker <tom@tombaker.org>
Date: Wed, 9 May 2012 11:01:01 -0400
To: Richard Cyganiak <richard@cyganiak.de>
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
Message-ID: <20120509150101.GA47671@julius>
On Wed, May 09, 2012 at 12:45:47AM +0100, Richard Cyganiak wrote:
> >> RDF vocabulary: A set of IRIs with clearly established referents intended
> >> for use in RDF graphs.
> >> 
> >> 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."  If you are saying that
most IRIs so declared routinely lack clearly established referents, I'm not
sure what you mean.

> > 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.

> >> The analogy with classes shows IMO that RDF Concepts is wrong and RDF
> >> Semantics is right. The IRI <http://xmlns.com/foaf/0.1/Person> *is* not a
> >> class, but it *denotes* a class.
> 
> That's correct, but has nothing to do with namespaces.
> 
> >    "The RDF namespace is also used as an XML namespace [XML-NAMES]..."
> > 
> >    ...where "RDF namespace" means (I think) "rdf: namespace IRI".
> 
> [[
> Definition: An XML namespace is identified by a URI reference [RFC3986];
> element and attribute names may be placed in an XML namespace using the
> mechanisms described in this specification.
> ]]
> http://www.w3.org/TR/xml-names/#dt-namespace
> 
> So yeah, the sentence you quoted should read: ?The rdf: namespace IRI is also
> used to identify an XML namespace [XML-NAMES] containing a number of
> additional element and attribute names??

+1

> > I note in passing that SKOS Reference [2] says:
> > 
> >    "The SKOS vocabulary is a conceptual resource identified by the
> >    namespace URI http://www.w3.org/2004/02/skos/core#..."
> > 
> > Would you disagree?
> 
> I wouldn't. That's consistent with everything above. The owners of the SKOS
> namespace IRI tell us that they decided that the IRI denotes the SKOS
> vocabulary.

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

> >> How is this?
> >> http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#referents
> > 
> > It looks pretty good to me!  I'm not sure what makes a referent "clearly
> > established", but maybe the vagueness is appropriate.  
> 
> Unfortunately, no one is quite sure about that, so vagueness is the only option.

Well put!

> > It could provide a place to clarify other
> > troublesome concepts in an informal, readable way, especially where there is a
> > *ahem* "range of opinions" among reasonable experts.  For starters, how about
> > "ontology"?  
> 
> Let me try.
> 
> [[
> 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"?  Does "ontology" mean
"OWL ontology"?  Is [1] an ontology?  Does its use of "owl:equivalentProperty"
make it an "OWL" ontology?  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 15:01:45 GMT

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