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   Re: RDF considered optional

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  • From: David Megginson <david@megginson.com>
  • To: Paul Prescod <paul@prescod.net>
  • Date: Thu, 18 Mar 1999 15:49:20 -0500 (EST)

Paul Prescod writes:
 > David Megginson wrote:
 > > 
 > >  > I took it the same way. But doesn't that violate the principle
 > >  > of XML as being self-describing?
 > > 
 > > First, there is no such published principle for XML itself,
 > > though the Namespaces spec provides an infrastructure for such a
 > > thing.
 > Debatably the principle of self-describing-ness is encoded in both
 > the XML declaration (unfortunately optional!) and the DOCTYPE
 > declaration.

Perhaps -- it's really a question of degree.  The XML declaration
tells you what the XML version is and may tell you about the intended
character encoding (the 'standalone' declaration is pointless and
should be ignored); the DOCTYPE declaration tells you what the root
element of the document is.  Neither of these, however, tells you
anything about what kind of XML document you're looking at.

 > > Second, it in no way violates it, because if you recognise the
 > > namespaces/elements being used, you can still figure out that you're
 > > dealing with RDF (and if not, fat lot of good they'll do you anyway).
 > Wouldn't it be useful for a generic RDF processor (e.g. viewer, search
 > engine) to be able to recognize RDF in arbitrary documents?

Of course it would be, but not everyone will want to define an
exchange format with rdf:RDF as the root element.  The presence of the 
rdf:about attribute can serve as a useful clue if it's there.

 > Personally, I do feel that the optional RDF element is a bad idea. I have
 > had many bad experiences with "implied declarations" like <!DOCTYPE HTML
 > ...> and <!SGML ...>. "Say what you are!" In this case the obvious way for
 > RDF elements to say that they are RDF elements without enforcing a
 > particular vocabulary would be to use attributes -- but that sounds like a
 > smelly old SGML-ish idea.

Yeah, stinky old architectural forms would be very helpful here.

All the best,


David Megginson                 david@megginson.com

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