Why validate? (was Re: Parser compliance)

Matthew Gertner matthew at praxis.cz
Mon Nov 22 13:29:03 GMT 1999


Here's at least one voice of absolute 100% agreement. "Running code" and
prose are patently not the only ways to express application semantics.
The current XML Schema draft already hints at things to come; if I can
state that a given element has content of type "positive integer" and
must be between 10 and 20, I am already expressing semantics that would
otherwise have to be implemented in procedural code. This and (IMHO) a
lot more can be expressed a lot more clearly and productively in a
declarative manner using schemas than in mucky "running code". It may
not be a sure thing, but it's certainly plausible that future XML
applications will be a combination of relatively low-level procedural
code and relatively high-level descriptive code (in the form of
schemas). There is no precedent for this, DTDs or other, which makes the
whole business quite exciting to think about. (And if anyone knows of
cases where people have tried approaches like this, in the SGML/XML
field or elsewhere, I'm VERY interested. Please let me know.)


Robin Cover wrote:
> While agreeing that SGML/XML DTD syntax is of limited value
> in supporting "validation," I think David Megginson and
> Tim Bray have somewhat short-changed the notion of
> declarative, constraint-based (ontologic/relational) semantics
> and corresponding (generalized, middle-tier) machine
> processing of constraint-based semantics within the "markup"
> framework.  I'm speaking of how things could be, not how
> they were (ISO 8879:1986) and are (XML 1.0) given
> the expressiveness of DTDs.
<rest snipped>

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