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"Rick Jelliffe" <email@example.com> wrote:
| From: "Jonathan Borden" <firstname.lastname@example.org>
|> I don't think it is possible to write a DTD that validates all legal
|> RDF documents and invalidates all documents that are not legal RDF.
An insight distilled from this opinion would be useful. That is, *why* is
a DTD unlikely? Or, what is necessarily possible in RDF/XML that the DTD
formalism can't capture? (Which might raise questions such as, why need
RDF/XML have its particular XML representation if, say, another equally
expressive one were possible to describe with a DTD?)
|> It *is* possible to do this with RELAX NG, however,
A useful basis for comparison in light of the above, indeed.
| [Without] *some* appropriate and independently designed and implemented
| executable schema language [...] you have to catch syntactic problems by
| checks at the semantic level, which may not be possible; better to catch
| semantic problems at the syntactical (schema) level as much as possible.
Structural validity as a necessary condition for semantic coherence (from
a practical point of view: i.e. achieving the latter without the former
*could* happen - from non-orthogonality, e.g. - but it's prudent to treat
that as an accident rather than as a designed feature.)