[Bug 14446] Conflicting statements on pre-override schema documents

https://www.w3.org/Bugs/Public/show_bug.cgi?id=14446

--- Comment #3 from C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com> 2012-01-03 01:05:15 UTC ---
Created attachment 1059
  --> https://www.w3.org/Bugs/Public/attachment.cgi?id=1059
Proposed schema-agnostic override transformation

As an alternative to modifying our rules about schema-validity of the input to
pre-processing steps, we could replace the current schema-aware transformations
with non-schema-aware transformations.  The attached version of the override
transformation is such a non-schema-aware transform; the versions of the
chameleon-include transform attached to bug 14448 are also non-schema-aware.

I do not have a principled objection to changing the text in the way suggested
in the bug description (not legible here at the moment, but recorded in
http://lists.w3.org/Archives/Public/www-xml-schema-comments/2011OctDec/0004.html).
 It may well be that the transforms are defined in such a way that only
schema-valid input is in fact guaranteed to produce schema-valid output; that
seems a possible, even plausible, consequence of the simplicity of the
transformations.  If I hesitate to make the change, and offer this
counter-proposal instead of drafting what the WG agreed upon, it is for two
reasons:  (1) the constraints on the input are a sore subject for some WG
members and I'd rather not reopen it if we can avoid it, and (2) although it
seems possible, even plausible, to believe that only schema-valid input to the
transforms can produce schema-valid output, only something resembling a proof
of that proposition could really carry conviction.  Such a proof would really
have to go almost line by line through the schema for schema documents arguing
that nothing in the chameleon or override transformations could render an
invalid document valid.  I haven't the time to attempt such a proof, and I
don't like to ask it of anyone else either.  (An ideal schema language ought to
lend itself precisely to proofs of this kind, but I fear the world may not yet
contain any ideal schema languages.)

So I make the counter-proposal of replacing the currently specified
transformations with non-schema-aware equivalents.

If the WG agrees, we could close this bug by adopting these non-schema-aware
transforms and leaving the prose text of the spec alone.

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Received on Tuesday, 3 January 2012 01:05:19 UTC