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   RE: RDF **vs** XML???

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  • From: David Megginson <david@megginson.com>
  • To: "'XML Dev'" <xml-dev@ic.ac.uk>
  • Date: Sat, 31 Jul 1999 21:27:00 -0400 (EDT)


Didier PH Martin writes:

 > OK, I badly expressed myself. Let's state it differently.
 > a) Wasn't XML with the purpose of allow you to create domain
 >    languages?

Sure it is, but you don't always want to create them directly on top
of XML; it's good to factor out common constructs into intermediate
layers of abstraction, to simplify the application designers' work.

 > d) Was RDF originally intended for meta data?

That was the initial motivation -- after all, the W3C isn't in the
business of general data exchange.  However, the spec editors realised 
that the distinction is arbitrary:

  The distinction between "data" and "metadata" is not an absolute
  one; it is a distinction created primarily by a particular
  application, and many times the same resource will be interpreted in
  both ways simultaneously.

 > Was then use a meta data domain language to encode data base records? You
 > could have encoded it with your own domain language. 

Yes, but then I lose the advantage of being able to use higher-level
APIs to access the information.  I could use UTF-8 without XML to
encode my documents, but I like that fact that XML parsers do most of
the work of building a tree out of a character stream; likewise, I
like the fact that RDF processors do most of the work of building
objects out of XML documents.

 > In fact, what is useful about rdf is not its elements but more its
 > schema part. When XML will have a schema language as good as the
 > rdf schema language or if both are united then I guess there is no
 > need to use rdf.

That makes very little sense to me.  Sure, a schema is interesting,
but an abstracted data-object layer is what will save people time and
expense in building XML systems for data interchange.

 > But the original intent of rdf is to add meta data information about
 > resources. This is why you have such construct:
 > <rdf:description about="http://www.netfolder.com/DSSSL">
 > The elements intentionally have the "description about" keywords.

rdf:Description is one particular class; RDF allows the creation of
new classes as well.

All the best,


David Megginson                 david@megginson.com

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