[Bug 5074] substitution groups not that strictly limited

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5074

           Summary: substitution groups not that strictly limited
           Product: XML Schema
           Version: 1.1 only
          Platform: Macintosh
               URL: http://www.w3.org/TR/2007/WD-xmlschema11-1-20070830/
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Structures: XSD Part 1
        AssignedTo: cmsmcq@w3.org
        ReportedBy: xan.gregg@jmp.com
         QAContact: www-xml-schema-comments@w3.org


The substitution group definition (below) says member names can vary widely but
that member types are "strictly limited". This may be technically true, but
seems to suggest a false sense of security in use of substitution groups. By
default, with no derivation constraints, a substitution group can transitive
include wildly different types. That is, a restriction step can remove all
optional content and an extension step could introduce completely different
content.

If my analysis is correct, please consider a milder statement and/or a warning
about unintentional extensibility.


---------------------
2.2.2.2 Element Substitution Group
All such members must have type definitions which are either the same as the
head's type definition or restrictions or extensions of it. Therefore, although
the names of elements can vary widely as new namespaces and members of the
·substitution group· are defined, the content of member elements is strictly
limited according to the type definition of the ·substitution group· head.

Received on Wednesday, 26 September 2007 00:29:02 UTC