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Model issues was: A certain difficulty

From: Tim Berners-Lee <timbl@w3.org>
Date: Tue, 29 Feb 2000 17:07:08 -0500
Message-ID: <02eb01bf8301$52ada1a0$84001d12@politburo.w3.org>
To: "David Megginson" <david@megginson.com>, <xml-dev@xml.org>, <www-rdf-interest@w3.org>

-----Original Message-----
From: David Megginson <david@megginson.com>
To: xml-dev@xml.org <xml-dev@xml.org>; www-rdf-interest@w3.org
<www-rdf-interest@w3.org>
Date: Friday, February 25, 2000 6:07 AM
Subject: Re: A certain difficulty


>Pierre-Antoine CHAMPIN writes:
>
> > I would not say that either !
> > I find the RDF model very simple and uniform (it's all about triples)
> > which makes its elegance... and for some people its weakness !
>
>Unfortunately, it's not about triples.  The only way to discover the
>true RDF data model is to reverse-engineer it from the XML, and it
>turns out that there are at least six components (not three) in each
>statement:
>
>  subject
>  subjectType (global id, local id, URI pattern)


The global ID and local ID are IDs, so the semantics should be the same.

A reference with a #fragmentID is taken as a reference to a part of  (or
view of) a document, while a reference without a # is taken as a reference
to the document.There is an unspoken problem that in the RDF spec a
reference to a subtree of an XML document containing RDF is taken to be a
erference to the RDF object.  .........(1)

The URI-pattern I agree is a big problem, and I think a lot of people would
have wished it not there. I wonder how many  systems implement it.  It seems
to me best to put it off to a level of logic above the basic RDF.
.............. (2)

>  predicate

>  object
>  objectType (literal text, literal XML markup, reference)


The object being the union of litteral types and reference to node is
reasonable: the object may be represented as a pair (type, value) for
example (or some other syntax or a pointer into a different part of memory
or a pointer to a self-typed object or whatever.)

You could argue (and people have i understand) that the same ought to hold
for the subject of course.   ............... (3)

>  objectLang


This is a mess pure and simpe: it is in the syntax and not in the model. How
did that happen? The syntax should not have bowed to the
internatoinalization community with a syntactic nod, but instead asked for
an RDF vocabulary for language. It should be removed from the synatax.
..............(4)
 My nurdlings on two ways of doing it are in
http://www.w3.org/DesignIssues/InterpretationProperties


>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).  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.


yes, abouteachprefix was a mistake in retrospect.

Here are 4 issues for an RDF M&S retrospecive post-Rec issues list!
Ralph or Dan Brickley was going to draw one up I think.

> > In the contrary, the XML syntax is a bit confuse, true.
>
>Yes, it is also unnecessarily confusing.
>
> > In my point of view, the problem comes from the recommandation
> > mixing modeling and syntaxic aspects (I won't mention semantic
> > aspects !)  in a way it's hard to differentiate them without some
> > RDF experience.
>
>The problem is that the model as presented is naively simple, and the
>WG failed to notice that the XML syntax is not based directly on that
>simple model.
>
>
>All the best,
>
>
>David
>
>--
>David Megginson                 david@megginson.com
>           http://www.megginson.com/
>
Received on Tuesday, 29 February 2000 17:08:02 GMT

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