Parser compliance

[Eric Bohlman]

On Wed, 17 Nov 1999, Richard Lanyon wrote:
> Not from me, that's for sure. But if people want validation from their XML
> processors (and people do, it would seem, possibly because so many XML
> books spend so much time talking about validity and DTDs), then we'd
> better give it to them or someone else will...

It seems to me that the reason why books and articles talk about
validation so much is the journalists and authors have gotten the idea
that it's important; if you believe the articles, the primary purpose of a
parser is to determine whether or not a document is valid (that idea may
be the result of a surface exposure to parsing theory, since an abstract
parser is in fact a language recognizer).

But in reality, the most a parser can do is syntactic validation; the
majority of applications need to do semantic validation using application
logic, and once you're doing that it's fairly easy for the application to
do syntactic validation at the same time.  Sure, parser-level validation
is a convenience; you can, e.g. do a getFirstChild on some element and be
assured that the child node is of the type you're expecting, but it's only
a convenience; you can always do a getNodeType yourself. Thus the main
roles for a validating parser appear to be in stand-alone syntax checkers
and structure-directed editors.



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