Weak DTDs

Sean Mc Grath digitome at iol.ie
Sat Oct 18 11:17:06 BST 1997

>W. Eliot Kimber wrote:
>> Peter has run head-on into one of the fundamental problems with DTDs as
>> currently defined by SGML (and XML): we want them to describe *classes* of
>> documents when they actually describe *individual* documents (and are
>> incapable of defining classes of documents except in very weak ways).
SGML establishes a one-to-one relationship between markup and DTD.
The instance - directly or indirectly - *names* its DTD.

However, a given instance can be gainfully parsed w.r.t.
many DTDs to achieve different effects - weakening contraints is one of 

To do this involves specifying at parse time - rather that at authoring time -
what DTD to use for the parse.

<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.

Sean Mc Grath

sean at digitome.com
Digitome Electronic Publishing

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