DTD confusion (was Re: Lotsa laughs)

David Megginson david at megginson.com
Fri May 28 16:20:35 BST 1999

John Cowan writes:

 > Lisa Rein scripsit:
 > > I thought that an XML v. 1.0-compliant application needed to be
 > > definable using a DTD (at this point) -- even if you didn't necessarily
 > > write one up for it -- that it *should* be possible to do so for any XML
 > > v 1.0-compliant application syntax. (like SMIL etc.) Is this NOT
 > > correct?
 > That is not correct.  As long as the XML documents are well-formed,
 > it is perfectly fine for there to be no DTD that describes them
 > both.  Instead, you can use any of the schema proposals, or English
 > prose, or French alexandrines, or what you will....

In fact, Lisa and John are both right, but they're slightly at

1. Any XML *document* that cannot be described by a DTD is not
   well-formed (I challenge anyone on the list to give me an example
   to the contrary).

2. An XML *document type* may contain restraints or allow structures
   that would be difficult or even impossible to model in a DTD.

The XML document type describes the characteristics that group certain
XML documents into a class -- these characteristics cannot always be
described using a DTD, and, in fact, may make the writing of a general
DTD for the whole class impossible.

All the best,


David Megginson                 david at megginson.com

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