On 2002-05-30 16:23, "ext Roland Schwaenzl"
<[log in to unmask]> wrote:
>> Could someone from DC-arch summarise how, if at all, they have seen
>> rdfs:isDefinedBy used in addition to its use as a relationship between a
>> term and a namespace?
>
> Dear Dan,
>
> "isDefinedBy" asks for a URI Identifier for a resource defining the subject
> resource
> - i.e. addresses a GENERIC concept of (namespace together with a URI
> identifier).
>
> It should be stated, that a subject resource, for which
> membership in a specific xml-namespace has been choosen (!), this choice
> DETERMINES the
> xml-namespace as the URI the subject resource "isDefinedBy".
I think folks are reading far too much into the term 'namespace'
and the relationship between namespaces used in RDF/XML and
the resultant URIs in the RDF graph model.
In particular, in the RDF graph model, there are no such things
as namespaces, qnames, etc. Those are, of course employed by
the RDF/XML serialization, so that predicate URIs can be
expressed as element and attribute names. But the RDF model
uses URIs, not qnames. RDF is not XML. Namespaces and qnames
are not significant to, nor have representation in the RDF
graph.
The value of rdfs:isDefinedBy is a URI denoting some resource
that defines the resource denoted by the subject of that
property. That's all. We don't know what the describing resource
is. It could be an RDF Schema instance. It could be an HTML
instance. It could be a PDF document. It could be a portal
to a relational database. We don't know. The semantics of
rdfs:isDefinedBy does not tell us.
Furthermore, one cannot determine the namespace/name partioning
of any arbitrary URI used in an RDF graph. It is not possible.
That partitioning is not retained. It is lost forever when the
RDF/XML is parsed into the graph. Also lost is the context of
the qname, whether it was an element name, an element-specific
attribute name, or a global attribute name. Cest la vie.
The bottom line is that XML and RDF have different naming
architectures. XML uses qnames, which are based on pairings
of namespace URIs and local names. RDF uses URIs. There is
a rather simple, unidirectional, and lossy transformation
employed by RDF to get from qnames to URIs, but qnames and
namespaces have no meaning in the RDF graph.
Namespaces and qnames for properties in RDF/XML are just a
means to an end, to serialize RDF statements and RDF ignores
the semantics of qnames defined by XML. Perhaps that's not
necessarily kosher, but that's how things are.
Cheers,
Patrick
--
Patrick Stickler Phone: +358 50 483 9453
Senior Research Scientist Fax: +358 7180 35409
Nokia Research Center Email: [log in to unmask]
|