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[Bug 12185] Conditional Type Assignment and substitutability

From: <bugzilla@jessica.w3.org>
Date: Fri, 03 Jun 2011 14:55:21 +0000
To: www-xml-schema-comments@w3.org
Message-Id: <E1QSVmT-0001c6-9K@jessica.w3.org>

--- Comment #14 from C. M. Sperberg-McQueen <cmsmcq@blackmesatech.com> 2011-06-03 14:55:20 UTC ---
I resist the change suggested in comment 13 because it takes a simple sentence
that is easy to understand, doubles its length, and makes it harder to follow. 
If a change of that kind is necessary, it's a fairly clear indication that we
have done a poor job of identifying the appropriate primitive notions, and the
correct solution is to do better.  Syntactic convolution is often a sign of
inadequate design work.  

I think it follows from the definition of type table equivalence that if
T1.{type table} is present and T2.{type table} is absent, they are not
equivalent.  It ought to be obvious that if neither type table exists, the rule
is satisfied, but XSD's attitude to null values is so poorly thought through
that I think SG is right that  it's not obvious and needs to be stated

Counter-proposal (still unnecessarily complicated and a sign of half-baked

4.6 S.{type table} is ·equivalent· to G.{type table}, if either ·present·.

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