xml-dev - Re: Question on ANY (its use in RDF)

[Chris Maden <crism@oreilly.com>]

[Marcus Carr]
> Roger L. Costello wrote:
> > I have a question about the ANY type.  It is my understanding that
> > an element defined to be of type ANY can contain any element that
> > is defined *within* the DTD (i.e., it cannot use elements that are
> > not defined in the DTD).  Correct?

Correct.

> My advice to anyone is never accept a DTD that uses ANY. The only
> legimate use I have ever seen for it is in an interim DTD during
> data conversion. It's a sloppy use of a sloppy mechanism - for
> example, would you really want to support an infinite number of
> nested rdf:Description elements? There is no preventing this - even
> the DOCTYPE element can be nested within itself.

However, remember that a document type is composed of its formal
specification *and* its prose specification.  Moreover, RDF is
explicitly intended for use with namespaces.  The RDF DTD expresses
constraints among RDF elements; using ANY in the content model of its
root was a good idea, just like HyTime uses ANY for most of its
content models.  Though I don't think the spec explicitly says so, RDF
is more akin to an architecture than to a document type, but without
the ability to rename element types.

-Chris
-- 
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