On 2002-06-03 11:56, "ext Roland Schwaenzl"
<[log in to unmask]> wrote:
> Dear Patrick,
>
> DC has fixed it's "namespace-policy" in
> http://dublincore.org/documents/2001/10/26/dcmi-namespace.
>
> About the usage of the namespace URI's it's saying:
>
> "All DCMI namespace URIs will resolve to a machine-processable DCMI term
> declaration for all terms within that
> namespace".
>
>
> Do you argue such use of namespace URI's is not legitimate?
Well, the debate over namespace documents, and whether a namespace
URI should resolve to some resource is currently unresolved and
under the scrutiny of the TAG, but my personal opinion is that
to allow a namespace URI to resolve to a document is to promote
a continued misunderstanding of the nature and purpose of
namespaces as defined by the XML Namespaces spec.
There are several issues, of which I'll only touch upon one here,
and that is the relation of a term to a namespace within the context
of RDF. Namely, there is none.
In an RDF graph, there are no namespaces, and there is no reliable
means to deduce the namespace that might have been used in the
original input RDF/XML serialization from a given term URI. Thus,
if an application is considering an RDF graph, there is no way
whatsoever for that application to obtain the "namespace" to which
that term "belongs" in order to even attempt to retrieve some
descriptive document that may define something about the term.
It can't be done. All you have are URIs, and any attempt to guess
at a namespace by looking at the lexical characteristics of the
URI, to e.g. strip of the maximal length of name characters from
the end, will not guaruntee you actually got the right namespace,
or any namespace for that matter. It's a guess. No more. And
solid, robust systems are not built upon guessing.
Furthermore, a given term may be defined by multiple resources, not
just one "namespace document", therefore the presumption that a
namespace dereferences to some resource that defines everything
about all terms grounded in that namespace is overly simplistic.
It doesn't work that way in the real world. Terms are resources,
and our knowledge about those resources can come from many sources,
most of which have URIs bearing no relation whatsoever to the
"namespace" URI used in their XML serializations.
There is an inherent incompatability between XML and RDF with
regards to namespaces -- namely that in the latter, they don't
exist. Again, there is no such thing as a namespace in RDF
semantics and there are no mechanisms in RDF for partitioning
terms according to namespace. Period. The presence of namespaces
in RDF/XML are an illusion. The namespaces have no semantic
reality. They are an editorial convenience, just like ENTITY
declarations. Once you parse the RDF, they are gone. Completely.
And knowledge models which define their vocabularies in
terms of specific namespaces have no support whatsoever from
RDF. Terms are terms are terms are terms and vocabularies are
made up of terms which need not have any URI in common in any
way. A single vocabulary may include terms from many "namespaces"
and a given model may employ multiple vocabularies.
Namespaces are simply punctuation. To try to make them into
identifiers for either vocabularies or models is a mistake. And
thus, to presume that a namespace URI would resolve to a single
resource which defines the terms of a single vocabulary is also
suspect.
Regards,
Patrick
--
Patrick Stickler Phone: +358 50 483 9453
Senior Research Scientist Fax: +358 7180 35409
Nokia Research Center Email: [log in to unmask]
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