Do I need to use a validating parser?

Steve Oldmeadow smo at
Wed May 5 05:21:38 BST 1999

----- Original Message -----
From: Joshua E. Smith <jesmith at>
To: <xml-dev at>
Sent: 05/05/1999 10:15
Subject: Re: Do I need to use a validating parser?

> Nonetheless, always up for the academic discussion, you can express the
> entire syntax of the LISP programming language in less than a page of DTD,
> I bet.  DTD's syntax is almost as expressive as that of XML itself.

I don't know LISP but how would you express scoping rules such as a locally
defined variable can only be accessed within the block it is defined such as
in Java?  I don't think this can be done using a DTD.  It could however be
expressed in some language marked up using XML.

I don't want to seem like I'm trying to rain on your parade or anything, I
was just wanting to save you some of the frustration I've been through.  If
DTDs were adequate there would be no push for another schema language.

Once you do come up with your language I'm sure you will still need to write
code to interpret it.  All the current tools are going to help you with is
to turn sentences in your language into an abstract syntax tree.  Actually
doing something with the tree is the hard part.  I came to the conclusion
that XML added very little and that you were better off just using the
traditional tools to generate a parser for your language.  One thing I toyed
with was whether a yacc like tool would be useful for XML-ish languages, in
other words it would help you generate parsers for languages that are marked
up using XML.  I'd be interested in your thoughts once you've come up with
your solution.

Steve Oldmeadow
Justice Systems Technologies

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