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The {attribute uses} property for an Attribute Group Definition schema component is defined as: "The union of the set of attribute uses corresponding to the <attribute> [children], if any, with the {attribute uses} of the attribute groups resolved to by the actual values of the ref [attribute] of the <attributeGroup> [children], if any." When performing the union operation, are duplicate attribute uses included in the final set? For example, consider the following: <xsd:attributeGroup name="fred" > <xsd:attributeGroup ref="bas:bill"/> <xsd:attributeGroup ref="bas:bill"/> </xsd:attributeGroup> <xsd:attributeGroup name="bill"> <xsd:attribute name="bob" type="xsd:string"/> </xsd:attributeGroup> When we compose the "set" of {attribute uses} for fred, should we only include the attribute use for "bob" once? Or does the final set of {attribute uses} contain 2 duplicate attribute uses for "bob" and result in an error according to constraint 2, section 3.6.6? See: http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001OctDec/0003.html
The WG decided (at the 12/20/2001 telecon) that the example is in error. An erratum will be created to clarify what it means to do the union operation to obtain the final {attribute uses}.
Discussed at 2007-05-18 telecon. The WG agreed to the decision mentioned in comment #1. The require wording comes dangerously close to schema composition and component identity. The WG didn't feel it is feasible to fix it in schema 1.1. The WG decided to marking this issue as LATER, meaning it *may* be dealt with in a future schema release after 1.1.