xml-dev - Re: Syntax and Semantics

[Marc.McDonald@Design-Intelligence.com]

I think the cases of actually processing the infornation in a document and
documents from different sources are often overlooked.


For example, a document with some MathML, ChemML, and HTML mixed together. A
DTD or schema may allow the syntax of the sections to be validated, but it
won't render the formula, molecule or text. The rendering is done by an
application which understands the semantics of the language involved.

There is no current specification for the cooperation of rendering engines
for MathML, ChemML and HTML - except perhaps through browser plugins and a
delegating XML browser. 

All namespaces provide is avoidance of ambiguity. All tying a namespace to a
schema adds is validity checking.

Consider documents of different namespaces that represent the same
information. Two companies may each have an product DTD or schema that
includes elements of SKU, ProductName, Description, and Price. Each uses
their own namespace. But each of these elements have the same meaning.

If the companies want to share information they must construct a namespace
they both use for the common elements. They also have to modify ALL of their
existing documents to use this new namespace.

This is like the class problem of languages like C++: Identity is determined
by class derivation, not form. Even if 2 instances are identical in form
they are not the same unless they are instances of the same class.

In the web context this is what drives 'standard' markup languages - create
your documents in this syntax so you don't have to modify it later when you
try to share it. Unfortunately we can't envision the entire set of markup
languages needed and if we could we would be establishing a central language
authority.

I would keep namespaces as they are - a means of resolving ambuigity. The
addition of a DTD or Schema doesn't really convey what an element means. The
embodiment of meaning is the application that processes the elements.

Marc B. McDonald 
Principal Software Scientist
Design Intelligence Inc
(www.design-intelligence.com)


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