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   RE: FW: Namespaces and DTDs

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  • From: "Didier PH Martin" <martind@netfolder.com>
  • To: <Marc.McDonald@Design-Intelligence.com>, <cbullard@hiwaay.net>
  • Date: Fri, 12 Mar 1999 20:19:59 -0500

Hi Marc,

Actually there is another representation of the information in the DTD
that is present: the application that uses the document. Unfortunately
the representation is in C++, Java or some other language. This
introduces a synchronization problem between the two.

The DOM api for instance gives you access to the parsed document tree,
but a sizable amount of independent code must be written to
essentially parse the DOM tree into the form the application needs.
The result is the structure is in 2 different forms, declarative and
procedural, which must be kept in sync.

You are right. but I can construct a DOM without any validation. The whole
point here is: if I need validation at the receiving end why not use SGML
which is more elaborate and necessarily need validation (because of the
possibility to have omittags). If however, we do not need validation at the
receiving end then, we are better to use XML that, because of its structure,
can be parsed without validation and then a DOM could be created for
procedural language consumption.

But you are right to say that from the serialized format I have to construct
a model (i.e. a structure) that interpreters can access. The DOM is the XML
way to do it and the grove for the SGML way (DOM and grove concept are
similar enough to reduce one to the other)

to become useful XML life cycle could be expressed like:

a) XML format creation: we need a DTD, so that the editor can validate the
document or simply prevent me to create an invalid document.
b) transport
c) receiving end: interpretation. The interpreter needs a parser. A
validating parser is not necesssary with XML, It seems that we have several
kinds of parsers:
	1- event driven
	2- function call within a loop
	3- DOM producer
d) The interpreter knows the semantic and do something.

In fact, XML rules do not convey semantics only syntax. Xpointers or Xlinks
are domain specific languages that add a semantic layer to XML. XHTML also.

In fact, all these concept where existing in the SGML world. Waht we gained
with XML compared to SGML is simplier parsing rule. So simple that
validation is no longer necessary to do a complete parsing operation. The
SGML syntax is more tricky because you need to tell the parser that some
markups are not with an end tag, thus, the need for a DTD which has the main
function to tell the parser some parsing rules like where a tag begin and
end. So, because of the "well formed" constraint we gained that now parser
do not a DTD to accomplish their task, the rule is clear on how a markup
begin and ends.

My conclusion:
we gained with XML the fact that a parser do not need to do validation.
Otherwise its only changing the XML extension to a sgml document. So, to go
from "mydocument.sgml" to "mydocument.xml" whitout really changing anything
except some minor modifications in the DTD declaration. That may be good for
marketing reasons but surely not for technical reasons.


Didier PH Martin

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