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From: "W. E. Perry" <firstname.lastname@example.org>
> ... It is therefore a choice to use the consumer's data structure
> and validity constraints, even if what is chosen comes from, or is approved by, the
> original document publisher.
> ...This is utterly at odds with the premise of validity, which
> insists that, however a document is connected to a particular schema, it must
> conform to that schema before it might legitimately be processed.
I think Walter is stating it too strongly, because of defining "validity" as being
only document-supplier validity. But validity can just as easily be incoming
QA (or process-internal pre-/post-condition checking) as it can be outgoing QC,
let alone public schemas. (In the case of Schematron, it seems that it is
almost always used for incoming QA and sometimes for blackbox testing of
processing, but rarely for public schemas. )
Also, I think Walter makes the assumption of draconian validation: that it is impossible
to process an invalid document. Some schema specs may go that route, but
it aint necessarily so. Indeed, one view of validation is that it involves
testing that a particular view of the data is available: that would seem to
fit in with Walter's general point on utility of ultra-loose coupling.