[rdfweb-dev] RDF parser vs. XML parser

Victor Lindesay victor at vicsoft.co.uk
Wed Aug 20 18:06:57 UTC 2003


Hi Diz,

RDF Parsers deserialise the RDF / XML into triples or statements, the
core object in the RDF data model. To perform the deserialisation they
will usually use an XML parser as you say. You may then query this graph
of triples by subject, predicate and object as in this pseudo code
method:
graph.GetStatements("http://www,some.com#some-bod",
"http://xmlns.com/foaf/0.1/knows", null)
to retrieve people who 'some-bod' knows.

XML parsers as I am sure you know already, allow you to query the XML
document according to its structure as the data is defined by that
structure. In an RDF document, XML is only used to 'mark-up' the
triples. Due to the variations in RDF / XML syntax where the same triple
can be marked-up in many different ways, an RDF document cannot be
processed solely using an XML parser or other XML technologies such as
XSLT with acceptable reliability.

Victor


> -----Original Message-----
> From: rdfweb-dev-bounces at vapours.rdfweb.org 
> [mailto:rdfweb-dev-bounces at vapours.rdfweb.org] On Behalf Of Dave Smith
> Sent: 20 August 2003 18:20
> To: rdfweb-dev at vapours.rdfweb.org
> Subject: [rdfweb-dev] RDF parser vs. XML parser
> 
> 
> Greetings,
> 
> I'm new to the RDF community and admittedly still wrapping my head 
> around everything. One thing that I'm not following (esp. on Edd 
> Dumbill's blog) is this distinction between "RDF parsers" and "XML 
> parsers". Obviously, an XML parser really only deals with syntax, not 
> semantics. But I've read in a couple of places (again, on 
> Edd's blog -- 
> particularly http://usefulinc.com/edd/blog/2003/8/8#13:13) that XML 
> "parsers" break when encountering unexpected (or missing) 
> elements. I'm 
> just not following the logic here, and so suspect that I don't 
> understand what is expected of an "RDF parser" (or processor).
> 
> Of note, we use XML parsers in Jabber and have been able to 
> deal quite 
> nicely with missing/unexpected elements.
> 
> I'm involved w/ the Jabber community and we are in the process of 
> looking at FOAF/RDF for describing the various entities on 
> our network. 
> It's quite promising really, but I need to understand how/if a RDF 
> parser is different from an XML parser. It seems like a RDF parser 
> would simply be something built on top of an XML parser (at least, 
> assuming we're using the RDF/XML encoding).
> 
> Thanks.
> 
> Diz
> 
> 
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