Hi Bill,
Bill said:
Obviously if we're talking about
different concepts we're unlikely to come to agreement on a common
"defintion". XML is most definitely a Context Free Language specified by a
Context Free Grammar. It is also definitely NOT a natural language.
Didier replies:
Gee and I wanted to close this thread :-) ...
Firstly, formal and non formal languages refer to a common base Noam
Chomsky's work. Noam Chomsky is a linguist.
Secondly, we are going beyond the focus of this list and I suggest that
anyone wanting to continue this conversation can email me directly to
martind(_at_)netfolder(_dot_)com(_dot_)
Thirdly, yes I know what a context free language (CFL) is and I don't
confound natural and formal languages. I - in my original message -
simplified the issue to make it easier to grasp for someone who asked a
question and make an emphasis that XML, per se, is a tool used to create
languages. Is a CFL a set of rules, somewhat but it's a high level
abstraction, and the XML specifications go beyond that (for instance,
definition of external entities - that call for an importation mechanism not
part of a CFL or CFG definition). Is a DTD a CFG grammar? Yes it is. Do XML
has several CFG properties? yes seen from a certain perspective. Can we say
that XML + schema languages are a set of rules that anyone can use to create
a language? yes. Can we say that a CFG language can do that? yes but with
little extras to make it practical and fill the gap between the abstraction
and the desired target language. Can we say XML is a strict CFL? No, the
specs go beyond that. Can formal languages be reduced to CFL, yes and some
notation languages exist for that and again, the XML recommendation goes
beyond a strict CFL notation. However the DTD part of the recommendation is
pretty close to a CFG definition since it leads to content models using
production rules (a CFL characteristic).
Conclusion: Can we say that XML as specified by W3C recommendation is CFG? I
would prefer to cite Derick Wood on that:
" The Standard Generalized Markup Language (SGML) is a meta-syntactic
language for the definition of Document Type Definitions (DTDs), which are,
essentially, extended context-free grammars in which the right-hand sides of
productions are similar to regular expressions and are called content
models. The Extensible Markup Language (XML) is, essentially, a simplified
version of SGML used to specify DTDs of Web-based documents."
I don't want to pollute this list with these issues, please email me
personally if you want to continue this thread.
Cheers
Didier PH Martin
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