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RE: A proposed solution to the RDF syntactic/semantic mapping pro blem (long)

From: <Patrick.Stickler@nokia.com>
Date: Thu, 21 Jun 2001 11:00:28 +0300
Message-ID: <2BF0AD29BC31FE46B78877321144043114B427@trebe003.NOE.Nokia.com>
To: jborden@mediaone.net, Patrick.Stickler@nokia.com, www-rdf-interest@w3.org
> > taking XML Schema '#' concatentation
> >
> >   <"http://foo.com/foo.html#bar", "bas"> ->
> > "http://foo.com/foo.html#bar#bas"
> >
> > (this surely violates the HTML MIME content type fragment 
> syntax, eh?)
> 
> You are under the mistaken impression that XML Schema directs such
> concatenation. XML Schema defines a mechanism to map _only_ 
> certain types
> defined in the XML Schema namespace. These types _all_ have IDs in the
> schema document. Again and again and again, XML Schema does 
> not define a
> general mapping of QName to URI, nor does XML Schema 
> generally _use_ URIs,
> rather it uses QNames to specify types.

Yes, agreed, but the point is that there is no explicit way
for RDF to get URIs for resources serialized by XML Schema
constructs.
 
> >
> > taking RDF simple concatenation
> >
> >   <"name:foo:aja", "varovasti"> -> "name:foo:ajavarovasti"
> >   <"name:foo:ajava", "rovasti"> -> "name:foo:ajavarovasti"
> >
> > (oops! now which is which?)
> >
> > There *is* no such automatic, reliable, consistent, and standardized
> > method of deriving an RDF resource URI reference from a namespace
> > and name pair.
> 
> The fact that this particular mechanism doesn't work does not 
> indicate that
> _no_ reliable method can be found. What are you suggesting?

Per my arguments in the original posting -- that because the
MIME content type cannot be known based on the namespace URI,
one cannot ever be sure that any possible scheme will always
produce a valid URI.

> > >
> > > I strongly consider _that_ a bug. There very much needs to be
> > > a MIME type
> > > _independent_ fragment identifier syntax (e.g.
> > > http://www.openhealth.org/RDDL/fragment-syntax)
> >
> > But that doesn't solve a thing! You *cannot* impose any specific
> > fragment syntax on any method of creating URI references 
> from namespace
> > and name pairs because that just further confuses the matter by
> > suddenly having URI references that are not valid URI references
> > according to the URI scheme or the presumed MIME content type
> > yet have strangeness in them.
> 
> huh? this syntax encapsulates _all known fragment identifier syntaxes_
> including: HTML, XML/XPointer.

Right. All *KNOWN* fragment identifier syntaxes. What about those
which are not known (as they have not yet been created) yet which
are equally valid schemes?
 
> > ...
> > > > "http://foo.com/bar.html#boo" + "bas" -> 
> "http://foo.com/bar.html#bas"
> >
> > What! How? My namespace is "http://foo.com/bar.html#boo", *NOT*
> > "http://foo.com.bar.html"!!! Just how do you determine that suddenly
> > the RDF identity of the resource is a fragment of some URI fragment
> > which is completely unspecified by the namespace URI fragment!
> > Namespace URI fragments are 100% opaque. Sorry, you can't use logic
> > to try to extract a *recognizable* prefix from one with which to try
> > to come up with a logical URI reference for a resource. Thirty lashes
> > with a wet noodle for you!

Sorry, forgot the smileys there ;-) ;-) ;-)

> where are your _or any other such_ rules written down? The "resource" in
the
> RFC 2396 sense is _always_ determined by the URI part of the URI
reference.

The web resource insofar as RFC 2396 defines it, but not as RDF defines
it (and there is discussion about just that at the moment if you check the
other threads).

> The fragment identifier is just a thingie that gets us part of a view on a
> resource. Where did some sort of mystical metaphysics get attached?

Because the "thingie" is the explicit focus of RDF. RDF does not make
statements about resources identified only by URIs. RDF makes statements
about
resources identified by URI *references*. In order to make statements
about resources identified by URI references, there must be an explicit,
regular, and reliable mapping from various serializations in which
identities
of referants are encoded, and single, complete, and valid URI references
within the RDF knowledge space (i.e. triples).

The problem is that in order to serialize identities of resources (RDF
Referants)
we must use multi-component representations rather than single monolithic
URI
references -- i.e a namespace and a name -- yet there is no standardized
mapping
between those two representations, monolithic URI reference and
namespace+name
pair.

> Why is this different from absolutizing a relative URI reference given a
> base URI? The algorithms for doing so are written down (RFC 2396), read
> them.

Relative URIs are not the issue here. URI References are.

> >...
> > If we ignore the issue of syntactic to semantic mapping, we
> > can see that the rest of RDF is doing pretty well. E.g. if one
> > has serialized RDF metadata that does not employ QNames for
> > any statements, resorting only to fully specified resource
> > URI references or literals, then everything is fine.
> 
> Such RDF serialization looking like what? How can you write down a triple
in
> RDF XML syntax (as opposed to the reification of a triple) without using a
> QName for the predicate?

Good point. My mistake. You can't. So this just further illustrates
how pervasive the problem is.

Cheers,

Patrick

--
Patrick Stickler                      Phone:  +358 3 356 0209
Senior Research Scientist             Mobile: +358 50 483 9453
Software Technology Laboratory        Fax:    +358 7180 35409
Nokia Research Center                 Video:  +358 3 356 0209 / 4227
Visiokatu 1, 33720 Tampere, Finland   Email:  patrick.stickler@nokia.com
 
Received on Thursday, 21 June 2001 04:00:37 GMT

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