[Bug 5079] Type tables and substitution groups

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5079

           Summary: Type tables and substitution groups
           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


It seems that type tables aren't used in the definition of type derivation or
substitutability, allowing for valid substitutions that subvert the type
constraints. For example,

<xs:element name="message" type="messageType">
  <xs:alternative test="@kind='string'" type="messageTypeString"/>
  <xs:alternative test="@kind='base64'" type="messageTypeBase64"/>
  <xs:alternative test="@kind='binary'" type="messageTypeBase64"/>
  <xs:alternative test="@kind='xml'"    type="messageTypeXML"/>
  <xs:alternative test="@kind='XML'"    type="messageTypeXML"/>
</xs:element>

<xs:element name="mixed_message" type="messageType"
substitutionGroup="message">
  <xs:alternative test="@kind='string'" type="messageTypeXML"/>
  <xs:alternative test="@kind='binary'" type="messageTypeString"/>
</xs:element>

Is this a problem?