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XML Schema Part 1 (Structure) and XML Schema Part 2 (Datatypes) seem to have different notions of "derived" for simple types. According to Part1, setion 3.14.6, Schema Component Constraint: Type Derivation OK (Simple), type unions and list extensions are NOT "derived" from their respective member types (but their member types are regarded as "derived" from the union type resp. list extension). This is in contrast to Part 2, which defines union types and list extensions as "derived" from their respective member types (2.5.2.2 and 2.4.2.3). The inconsistent semantics of "derived" can lead to confusion among schema authors, in particular when working with substituion groups, instance type overriding, and redefinitions. We suggest to drop the term "derived" for type unions and list extensions in XML Schema Part 2 and to replace it with the term "constructed". This would also affect the classification of the built-in types NMTOKENS, IDREFS, and ENTITIES, which are no longer "derived by list" but "constructed by list". See: http://lists.w3.org/Archives/Public/www-xml-schema-comments/2002JulSep/0014.html Ashok's response: http://lists.w3.org/Archives/Public/www-xml-schema-comments/2002JulSep/0022.html
Discussed at the Sept. 27 concall. RESOLVED: to defer R-170 to 1.1. RQ-120.