Using XMLSchema.xsd in application schemas

The WXS schema-for-schemas contains a number of components that could usefully occur in XML instance documents, particularly concerning simple type definitions. In principle it should be possible to accomplish this with a simple <import> of the S4S into an application schema, but standard tools behave inconsistently. 
There appears to be two issues:
1. the "magic" simple types mean that the S4S is not a completely valid WXS schema;
2. even though it is theoretically OK, importing the S4S appears to confuse some processors when definitions attempt to override "private" definitions of schema components used by the processor. Some guidance in the spec is required to resolve this. 

There was a brief thread discussing this issue on xmlschema-dev - see http://lists.w3.org/Archives/Public/xmlschema-dev/2003Nov/0048.html

I request that this issue be considered by the W3C XML Schema working group, perhaps for WXS 1.1. 

Simon Cox

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Simon.Cox@csiro.au  CSIRO Exploration & Mining
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