[Bug 11354] Mentions of "override" outside of the override section

http://www.w3.org/Bugs/Public/show_bug.cgi?id=11354

C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needsDrafting               |needsAgreement
         Depends on|                            |12184

--- Comment #3 from C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com> 2011-03-02 21:05:51 UTC ---
I'm beginning to believe that the WG needs to re-open this issue because our
resolution was based on an inaccurate premise.  In particular, we were
operating on the belief that the override transform is defined in such a way
that eventually, after performing the transform for each document in the target
set of a given override element, one would have a set of schema documents none
of which contain any override elements.  It would be these schema documents
which are subject to the schema-document constraints.

But as Michael Kay has pointed out in bug 12184, the override transformation is
not guaranteed to eliminate all occurrences of the override element.  On the
contrary, it may increase the number of override elements, since it transforms
every include element into an override element.  This should not be a surprise,
since it was made explicit in the design discussions for the override facility
that the transform would turn cycles of includes into cycles of overrides.  But
the shorthand description that 'the semantics of override can be reduced to the
semantics of include' (which is true, I think, as far as it goes) led the WG
into the false belief that 'the override transform transforms all overrides
into includes'.

Since the transform as currently specified does not eliminate all override
elements, we cannot as things stand plausibly eliminate override elements from
the syntax overviews in the spec (which means that bug 11179 also needs to be
revisited) or from the schema for schema documents.  

I think our options include at least:

1) Reverse our decision on this issue and bug 11179.  Accept that override
elements must be handled in the schema for schema documents, in syntax
overviews, and in discussions of where elements can appear.  Ensure that all
constraints on schema documents make sense in the presence of override.

2) Respecify the override transform to change the way it propagates an
override.  In particular, make it guarantee that a simple-minded process of
applying the transform will ultimately produce a set of documents without any
override elements.  

The second option has the unhappy property that almost every time I look at it,
it seems to be within reach, and every time I try to sketch the transformation
required, I find that it either doesn't eliminate overrides after all, or that
it fails to provide the functionality required by our resolution of bug 6021.

3) Forbid cycles in override and include.

In the absence of cycles, there is an override-free set of schema documents
corresponding to any override target set.

For the reasons just given, I'm (unilaterally) changing the status of this
issue from needsDrafting to needsAgreement, and marking it as dependent on bug
12184.

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Received on Wednesday, 2 March 2011 21:05:53 UTC