[Bug 5905] New: vc:typeAvailable and vc:typeUnavailable

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5905

           Summary: vc:typeAvailable and vc:typeUnavailable
           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


I'm struggling with the semantics of vc:typeAvailable and vc:typeUnavailable.

One might expect that one can write two alternative elements, one with
vc:typeAvailable="A B C" and one with vc:typeUnavailable="A B C", and exactly
one of the two will be chosen. But this is not the case. The first attribute
causes the element to be used if and only if ALL the types are available, while
the second causes it to be used if and only if ALL the types are unavailable.

I think it would be much more useful and intuitive for these attributes to be
complementary. I think that vc:typeUnavailable should cause the element to be
used if ANY of the types is unavailable. That is, it is ignored if and only if
all the types are available, which means changing the wording to:

vc:typeUnavailable = T, where every item in the ·actual value· T is the
expanded name of some type definition ·automatically known· to and supported by
the processor

and similarly for vc:facetUnavailable. [We might want to spell out that the
universal quantifier is always true for an empty set.]

In the common use case where the list is of length one the meaning is
unchanged.


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Received on Tuesday, 29 July 2008 15:06:28 UTC