RDF is painfully simple, conceptually. And Lisa is correct in saying that
the syntax is (IMHO unnecessarily) kinda ugly; I think there are good
reasons to expect improvement.
But it is easy to tell if something can easily be made into RDF. Here's
the test: if what you are building can be expressed as a bunch of 3-tuples
(object, propertyname, propertyvalue)
then it's RDF-able. Otherwise it's not.
E.g.
(document, rootType, HTML)
(elementType IMG, takesAttribute, SRC)
(attribute SRC, valueType, URI)
(attribute BORDER, defaultValue, "1")
(entity copy, value, "©")
(entity xml-spec, systemID, "http://www.w3.org/TR/REC-xml")
are all easily RDF-able.
I think the only thing in DTD's that are not trivially RDF-able are
content models. They *are* RDF-able, but you have to use some of the
"Seq" machinery, which I find awkward. In fact *every* attempt so far
(the old DSD stuff, XML-Data, etc) to express content models in XML has
come up verbose and unreadable compared to good ol' 8879 DTD notation.
I think there's a better way, and want to see what xml-dev can come up
with. -Tim