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

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sun, 21 Oct 2001 21:41:20 -0400
To: bwm@hplb.hpl.hp.com
Cc: www-rdf-interest@w3.org, simeon@research.bell-labs.com
Message-Id: <20011021214120T.pfps@research.bell-labs.com>
From: Brian McBride <bwm@hplb.hpl.hp.com>
Subject: Re: a new way of thinking about RDF and RDF Schema
Date: Sun, 21 Oct 2001 23:24:38 +0100

> Peter F. Patel-Schneider wrote:
> 
> [...]
> 
> >>>
> >>Most RDF parsers are built on a standard XML parser.  This is true of SiRPAC, 
> >>RDFFilter, ARP and Redland's parser.
> > 
> > How can this be?  RDF is not XML. 
> 
> RDF/XML (to name the xml syntax for RDF, not the RDF datamodel) is a subset of 
> XML.  It conforms to XML syntax.  Parsers deal with syntax.

RDF/XML is not a subset of XML.  parseType=literal is in M&S.  It has been
in from the beginning.   parseType=literal requires that its context not be
processed by an XML parser.    parseType=literal elicits the most
puzzlement from XML people that I try to explain RDF to, even ignoring the
current debate over its details.

> > How do they handle parseType?  An RDF
> > system that handles parseType has to get its hands on the raw bits, before
> > an XML parser sees them.
> 
> That statement is not correct.  RDF parsers such as RDFFilter, ARP and SiRPAC 
> are built on top of an XML parser.
> 
> Typically they operate in streaming mode, where the XML parser outputs a stream 
> of SAX events which are interpreted by the RDF parser.

Then how can they handle parseType=literal?  I really don't understand how.

> parseType="Literal" is something the RDFCore WG is, err ..., working on, right 
> now.  Its not really clear exactly how to handle this.  Most parsers currently 
> turn it into a Literal, but there is no agreement on exactly what Literal. 
> Other suggestions include generating an RDF representation of the infoset 
> representation of the embedded xml.

Yes, but how?  Once XML parsing is done you no longer have the original
bits to be turned into a literal.

> But whatever the outcome of that discussion, I'd expect RDF parsers to continue 
> to be built on XML parsers.  Am I missing something?

I just don't see how there is any way that parsetype=literal can be done
after XML processing.  


> >>><rdf:Description rdf:type="a:b"/> is not valid RDF because a:b is not a
> >>>literal, not (just) because QNames are not allowed as attrib values. 
> >>>
> >>This is a nit, but the rdf:type attribute is a special case in RDF.  The value 
> >>of the attribute is the URI of a resource, not a literal.  You may wish to add 
> >>that to your list of mistakes in RDF.
> >>
> > 
> > Precisely.  Therefore RDF can't use the abbreviation you wanted.
> 
> You might like to have a look at the following para in M&S
> 
>    http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-part#227

You are correct.  Yet another special case in the syntax.  

> Brian

Peter F. Patel-Schneider
Received on Sunday, 21 October 2001 21:42:07 GMT

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