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Hello,

is the Document Type Definition (DTD) part of an SGML text interchange?
To specify my question: does a software product, e.g. a publishing
system, which tells to be able to use SGML format, have to be able to
read an SGML document and *any* DTD? As I understand, then it has to 
read the DTD, which is something like a grammmar for me, and then parse
the text, using this DTD.

I ask this, because a software manufacturer tells me, I have to send the
DTD for my special problem to him, and then he will return a special 
filter for documents which behave like this DTD. So anytime I have a new
type of document, I have to buy a new filter. 

Is there something inside the SGML definition, which I don't have at
my desk, sorry, which tells me that a DTD is part of an SGML document?
What is the idea of the CALS standard with SGML text exchange?

Thanks,
Carsten Schiers
Deutsche Airbus GmbH
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