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RE: What is RDF for? (Was: What are Web Services for?)

• To: "Matthew Gertner" <matthew.gertner@s...>
• Subject: RE: What is RDF for? (Was: What are Web Services for?)
• From: "Manos Batsis" <m.batsis@b...>
• Date: Wed, 1 May 2002 11:20:25 +0300
• Cc: <xml-dev@l...>
• Thread-index: AcHwPpFns/5D1bH2Rf2CCOL+T1RiHgAo3wrA
• Thread-topic: What is RDF for? (Was: What are Web Services for?)

> From: Matthew Gertner [mailto:matthew.gertner@s...]

Manos Batsis wrote:
> > RDFS defines what properties are appropriate for a
> > certain type of recourse and what kinds of values it can 
> hold. Because
> > RDF Schema does not validate structures but the model 
> behind them, it
> > can be used to validate even non-XML (i.e. n3) formats that 
> > can describe
> > an RDF graph.
> 
> If we agree that XML adoption is going to drive the semantic 
> web, then the
> benefits of smoother integration with XML far outweigh the 
> advantages of
> annotating other formats.

What most know as RDF, is just a serialization of the RDF model to XML. RDF is a graph, not just a tree.


 
> > What keeps you from doing that today using both RDF(S) and 
> > XSD (or any
> > other)? I cannot understand why you wish to merge two 
> > different things
> > in one place.
> 
> Too much duplicated work.

Can you provide a small example of the same type in RDFS and XSD and point to the duplicated stuff?


> And I'm not proposing merging them 
> in the same
> place, I'm proposing using a separate annotation file (or 
> several, for that
> matter).

RDDL should be able satisfy you on this aspect. 


> > But you did not attached DC semantics to an element type. 
> > Vanilla XML
> > interprets namespaces in a very different manner than RDF. My 
> > point here
> > is that when parsing RDF, you get an RDF graph. Getting in 
> > the process
> > of extracting the annotations you need to validate the 
> > graph makes you
> > dependent on the XML parser you use for XSD validation. Why 
> > having such
> > dependencies?
> 
> I'm interested in your comment on namespaces. Can you 
> elaborate on that?

XSD (or vanilla XML in general if you preffer) uses namespaces to avoid coalisions of identical node names, or to group  a vocabulary etc. The model behind an XML node as 

<elem xmlns="http://www.foo.org/ns" />

is an [Element Information Item] with the following properties:
[namespace name] "http://www.foo.org/ns",
[local name] "elem",
[prefix] null,
[children] empty set,
[attributes] empty set,
[...]etc. 

My point is vanilla XML contains no semantics; just a common iterpretation scheme called the Infoset.

On the other hand, RDF(S) adds a semantic layer on top of namespaces: they are used to link a resource with the RDF Schema that defines it. The model behind RDF holds no namespaces, just URIs and literals. For example, the name rdfs:Resource expands to the resource http://www.w3.org/2000/01/rdf-schema#Resource 

No namespaces etc. Actually, nothing to do with XML...

 
> As far as the parser is concerned, I imagine that you could 
> extend a SAX
> parser with a module that understands the annotations 
> (basically just the
> RDF model expressed using a more natural XML-schema-related 
> syntax) and
> exposes the model to the user (using RDF mechanisms, as far as I'm
> concerned).

I am sure most would not want to extend a parser for this task.


> I don't really see why the parser itself would need to do
> anything besides validate the document and generate SAX events.

Depends on what you mean "validate" ;-)

 
> OK, I guess I meant "an entirely new syntax" rather than "an 
> entirely new
> model".

If you come up with a better XML syntax to cover the RDF graph, I'm sure most of us would be interested in it.


> > RDFS is much better in this aspect; because it implements OO design
> > structures. Throw a new property in the basket, associate it with a
> > Class and voila. Global, non-document centric awareness.
> 
> This is exactly the view that I am arguing against. We *want*
> document-centric awareness!

Could you provide an example? I was going to argue with this but I suspect we use the same term "document centric" with different meanings. I meant that in my world, this can be used in and for any document; it's global because of URIs.

Cheers,

Manos 

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