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Re: more on a new way of thinking about RDF and RDF Schema

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 15 Oct 2001 22:14:48 -0400
To: melnik@db.stanford.edu
Cc: www-rdf-interest@w3.org
Message-Id: <20011015221448W.pfps@research.bell-labs.com>
From: Sergey Melnik <melnik@db.stanford.edu>
Subject: Re: more on a new way of thinking about RDF and RDF Schema
Date: Mon, 15 Oct 2001 17:04:13 -0700

> Peter,
> 
> I'm lost. Are you trying to provide a model theory for DOM trees (or
> XQuery data model etc.)?

As indicated below, my intent was to tie RDF into other W3C standards, in
this case XML and XML Schema, as embodied in the XQuery Data Model.  If you
do this then you don't need an RDF parser.  The core of a core RDF processor,
including entailment, can be written in about 250 lines of ML code, using
a separate processor for XML and XML Schema that produces an XQuery Data
Model.

> As to "dumbing down" triples to pairs (using EXT, CEXT), I think there
> is no doubt that binary relationships is all you need, in theory. I
> think the main benefit of a model theory is that is clarifies the
> terminology and definitions. IMO, the "binary" approach is harder to
> understand.

To handle more of the XQuery Data Model, I had to move to interpretations
without edge labels, which are more complex and admittedly harder to
understand, but more general. 

Edge-labelled models cannot handle things like

<foo>
  7
  <bar>5</bar>
</foo>

which are allowed in XML.

> As to datatypes: as far as I understand, you suggest to map a lexical
> token (element of L) to a set of data values (DV) using XTS. For
> example, XTS("05") = { (int)5, (double)5.0 }. How useful is that? I
> think for datatyping it is essential to decide what type a literal has
> in each specific triple. Does the notation below provide this means?

Sure, in the RDFS version, you can provide typing via ranges.  I'm just
allowing for untyped stuff, or stuff that is not typed within XML Schema.
I'm not aware of any other model-theoretic way of handling untyped literals.

Typed stuff works as you would expect.  For example, in
	<foo xsi:type="xsd:integer">07</foo>
the xsi:type="xsd:integer" will restrict the interpretation of 07 to the
integer 7.

> Sergey

peter

> "Peter F. Patel-Schneider" wrote:
> > 
> >         A Radical Reinterpretation of RDF and RDF Schema plus Datatypes
> > 
> >                 Peter F. Patel-Schneider
> >                 Bell Labs Research

[...]

> > Over the last little while I've been looking at XML Infoset, XML Schema,
> > and the new RDF data model.  I put together a different way of looking at
> > RDF and RDF Schema that places all RDF and RDF Schema processing after the
> > creation of the XQuery data model.  It also moves interpretations closer to
> > the XML way of looking at the world.
> > 
> > Supppose we really believed that RDF should use other W3C standards.  How
> > could we do that?  Well one way would be to have all initial processing of
> > RDF documents be done by other tools, and only do the RDF processing after
> > they are done.  (Note that DAML+OIL actually does a version of this, as its
> > input is a collection of RDF triples.)
> > 
> > Just what sort of processing should be handled by other standards?  There
> > are several potential answers to this, but the standard that does the most,
> > I think, is the XQuery Data Model.  This data model results in a tree, with
> > a considerable amount of processing having being done on the tree,
> > including XML Schema processing.  So the ``input'' to RDF will be (a slight
> > generalization of) the XQuery Data Model.
> > 
> > The next issue to be addressed is how differences between the XQuery Data
> > Model and RDF are to be handled.  There are several serious differences
> > that need to be addressed here.  First, the XQuery Data Model has an order
> > on the children of a node.  I propose that this be ignored.  Second, the
> > XQuery Data Model does not have edge labels.  I propose to move closer to
> > the XQuery Data Model by using two unlabeled edges with a ``label'' on the
> > middle node instead of a labeled edge.  This change means that there are
> > some interpretations that do not correspond with RDF interpretations.
> > Third, there is lots of information in the XQuery Data Model that is not in
> > the RDF model, such as comments and processing instructions.  I propose to
> > ignore almost all of this information.  Fourth, there are aspects of
> > RDF that are not in the XQuery Data Model, such as node IDs.  I propose to
> > extract this information from the XQuery Data Model in much the same way as
> > it is proposed to be encoded in XML by the RDF M&S.
Received on Monday, 15 October 2001 22:15:28 GMT

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