[Bug 2224] R-232: Vacuous Redefinition

http://www.w3.org/Bugs/Public/show_bug.cgi?id=2224

           Summary: R-232: Vacuous Redefinition
           Product: XML Schema
           Version: 1.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XSD Part 1: Structures
        AssignedTo: ht@w3.org
        ReportedBy: sandygao@ca.ibm.com
         QAContact: www-xml-schema-comments@w3.org


In June 2003, the XML Schema WG briefly discussed cases like the following: 

XSD1:
<schema ...>
<complexType name="CT">
...
</schema>

XSD2:
<schema ...>
<redefine schemaLocation="XSD1">
<!-- CT in XSD2 is vacuous restriction of CT in XSD1 *-->
<complexType name="CT">
 <restriction base="CT"/>
</complexType>
</redefine>
</schema>

XSD3:
<schema ...>
<import schemaLocation="XSD1"/>
<import schemaLocation="XSD2"/>
</schema>

Several questions arise: 

1. is this legal or not, in XML Schema 1.0? 
2. regardless of the answer to (1), SHOULD this be legal in XML Schema? 

One position one could take is that since the CT of XSD1 and the CT of XSD2 are 
as similar as one can make them (same name, same extension), the double import 
really should be legal. 

Another possible position is that if one wanted them to be identical one would 
not have redefined CD in XSD2 -- just as vacuous restrictions can be used to 
block certain substitutions by imposing a certain structure on the type 
hierarchy, so the vacuous restriction here should be allowed, and should not be 
treated differently from a non-vacuous restriction. 

When this came up in June, some WG members offered an analysis of this case 
which led them to conclude that the example is not legal; I never understood 
the details. Can anyone expound? 

Depending on what the WG decides to do, this topic might turn into an error 
report on 1.0 or a requirement for 1.1, or a no-action-needed. 

See:
http://lists.w3.org/Archives/Public/www-xml-schema-comments/2003JulSep/0062.html

Received on Wednesday, 14 September 2005 19:24:39 UTC