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   Re: Why validate? (was Re: Parser compliance)

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  • From: David Megginson <david@megginson.com>
  • To: xml-dev@ic.ac.uk
  • Date: 18 Nov 1999 08:26:45 -0500

ht@cogsci.ed.ac.uk (Henry S. Thompson) writes:

> Maybe I was overly influenced by the fact that my first exposure to
> pointy brackets was in the context of SGML, but I think validation is
> pretty fundamental.

I don't think that anyone is arguing against the usefulness of
validation -- Tim's point is DTDs and other formal schemas alone
supply only a small subset the validation necessary for any
real-world information exchange.

> A DTD is like a contract, it helps both clients and service
> providers to maintain a satisfactory working relationship.

It's a very simply contract, though; consider the following DTD:

 <!ELEMENT song (title, composer)>
 <!ELEMENT title (#PCDATA)>
 <!ELEMENT composer (#PCDATA)>

Here's a document that's valid according to that DTD, and that doesn't 
fiddle with the DTD in its internal subset:

 <?xml version="1.0"?>
 <!DOCTYPE song SYSTEM "song.dtd">
  <title>David Bowie</title>
  <composer>Let's Dance</composer>

As Eliot, Tim, and I have all mentioned (in different contexts), the
primary contract *has* to be the human readable documentation, even
though the DTD is useful for detecting a certain subset of problems.

All the best,


David Megginson                 david@megginson.com

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