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[Bug 6163] New: Attribute Wildcard Union

From: <bugzilla@wiggum.w3.org>
Date: Wed, 15 Oct 2008 13:20:38 +0000
To: www-xml-schema-comments@w3.org
Message-ID: <bug-6163-703@http.www.w3.org/Bugs/Public/>


           Summary: Attribute Wildcard Union
           Product: XML Schema
           Version: 1.1 only
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Structures: XSD Part 1
        AssignedTo: cmsmcq@w3.org
        ReportedBy: mike@saxonica.com
         QAContact: www-xml-schema-comments@w3.org

(1) The Note:

Note: If a wildcard union is inexpressible, any rule requiring that one
Namespace Constraint be that union cannot be satisfied.

is unnecessary, because there is no such rule.

(2) The final paragraph is unnecessary, because there is nowhere in the spec
that takes a wildcard union with more than two Namespace Constraints as
operands. (Wildcard union is used only when one type T is derived by extension
from another type B, and this involves only two wildcards.)

(3) Rule 4 in the final list is structurally misplaced. Given that the
definition has adopted the style "O is the union of O1 and O2 if and only
if...", the notion that the union of O1 and O2 might not exist cannot logically
be part of this definition. I would move it right up to the front, and then
qualify the rest by "If the union of O1 and O2 is expressible, then O is the
union of O1 and O2 if and only if..."

(4) Finally, and more substantively, I'm having trouble seeing why the wildcard
union should be inexpressible in the circumstances stated, or indeed in any
circumstances. The union, surely, should match everything that is matched
either by one wildcard or by the other or by both. The union could be defined
either extensionally (treating "defined" as simply a synonym for the list of
names of global attribute declarations present in the schema), or intensionally
(if one wildcard excludes "defined" attributes and the other does not, then the
union does not exclude "defined" attributes).

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Received on Wednesday, 15 October 2008 13:20:48 UTC

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