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   Re: A certain difficulty

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  • From: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
  • Date: Tue, 29 Feb 2000 16:32:50 +0100

"Perry A. Caro" wrote:
> David Megginson wrote:
> > it
> > turns out that there are at least six components (not three) in each
> > statement:
> >
> >   subject
> >   subjectType (global id, local id, URI pattern)
> >   predicate
> >   object
> >   objectType (literal text, literal XML markup, reference)
> >   objectLang
> >
> > These are not simply syntactic artifacts -- it's information that
> > *must* be exposed through any RDF API, and thus, part of the core
> > model, independent of the peculiarities of the XML markup (note that
> > I'm assuming that bagID, etc. are predigested).

I guess I locate the limit between syntax and model auite further than David :
the syntax is the job of the RDF parser (a layer over an XML parser)
whose output is a direct labeled graph.
the model is the job of an RDF agent(?) which will handle this graph.
So my view of the model includes mainly subject/predicate/object :

subjectType : URI, in every case
objectType : sure there should be resource/literal distinction
 I already argued on this list that literal ARE resources, and should be treated in the same way
objectLang : only for literals, which I don't like !
 anyway, if literal where handled as resources, xml:lang wpuld be a property of them,
 which could be expressed by another triple

> Hear, hear!  It's misleading to talk about Statements as "simple" triples.
> They are either triples where each member is a complex object with various
> attributes, or they are N-tuples of several fields, some of which are
> optional or default.

I'm not sure I get it, Perry...

> By the way, you forgot "objectWhiteSpace", a field like objectLang, whose
> value is either "default" or "preserve".  This is crucial to correctly
> handling the xml:space global attribute.

another property of literal-resources, in my point of view.
But you're right, as long as literal are treated as an exception and can not have properties,
xml:lang and xml:space raise a problem !

> > The URI patterns
> > (aboutEachPrefix), especially, make it much trickier to do any
> > relational database implementation of RDF, since you the set of
> > possible subjects is open.

this is the job of the parser, which is, once again, syntax dependant.
This is not, IMHO, part of the model (since the parser only has to produce result triples)
But we agree, this is a disturbing feature, hard to implement in a distributed architecture like the web !



--- Quid quid Latine dictum sit, altum viditur
    Whatever is said in Latin sounds important.

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