[Bug 6561] Type Substitutable in Restriction

http://www.w3.org/Bugs/Public/show_bug.cgi?id=6561





--- Comment #5 from C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com>  2009-02-25 03:36:45 ---
Created an attachment (id=636)
 --> (http://www.w3.org/Bugs/Public/attachment.cgi?id=636)
Alloy model of contextual determination of type table

A further note here on the quest for an example in which there is
a type which for which the mapping from QNames (or element
instances) to context-determined type tables is not a function.
I continue unable to construct such an example.

I attach an Alloy model of this part of the spec.  I have used
this model to try to findt a schema in which there is some
complex type which does not uniquely determine a
context-determined type table for each possible QName.  The Alloy
Analyzer has searched all models with seven or fewer complex
types and seven or fewer element declarations, without finding a
case of a context-determined type table which is not uniquely
determined.

While it is suggestive, Alloy's failure to find a counter-example
is not, of course, conclusive.  There may be counter-examples in
larger schemas.  Or the Alloy model could be faulty in its
description of XSD's rules.  Corrections and examples of
problematic schemas welcome.

My experiments with this model have led me to believe it might be
more nearly correct to rephrase the note which currently reads

    Note: The constraint Element Declarations Consistent
    (§3.8.6.3) ensures that even if E matches more than one such
    declaration D, there will be just one context-determined type
    table.

to make it read

    Note: The definition just given, together with the constraint
    Element Declarations Consistent (§3.8.6.3) and the rule
    ensuring that no two top-level element declarations have the
    same name, ensures that even if E matches more than one such
    declaration D, there will be just one context-determined type
    table.

I doubt, however, that the increased correctness is worth making
the note wordier and harder to follow.


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Received on Wednesday, 25 February 2009 03:36:54 UTC