Weak DTDs

Paul Prescod papresco at technologist.com
Sat Oct 18 15:40:16 BST 1997

Sean Mc Grath wrote:
> <Statement InvititationForTrouble=TRUE">
> HyTime allows parsing w.r.t. a meta-DTD via HyTime aware parsers. However,
> I think there are many occasions when there is nothing "meta" involved. Just
> a desire to parse w.r.t to an alternative schema. Not a meta-schema - just
> a different schema.
> </Statement>

That's absolutely true. And ARCHFORMS absolutely allow this. That is why
calling them "meta-DTDs" is very misleading. The archform feature allows
you to specify a mapping from elements to element types using
attributes, rather than GIs. This is very similar to CONREF except that
you can use minimization features like #FIXED, default values, #CURRENT,
LINK and also some archform specific minimization features to make the
mapping without putting an attribute on every element the way you must
with GIs. 

In fact, sometimes you can make the mapping without putting an attribute
on any elements at all. Then you can seem to set up a mapping between
element types in one DTD and element types in another DTD. Thus you have
the illusion of a DTD to DTD relationship rather than an instance to DTD
relationship. That's when archforms seem like a "meta-DTD". But in the
general case where you ignore minimization, archforms are not really
"meta" anything. They are alternate DTDs validated according to
attribute values, not GIs.

 Paul Prescod

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