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In the section titled 'Schema Component Constraint: Particle Restriction OK (Elt:Elt -- NameAndTypeOK)', the following is mentioned: "For an element declaration particle to be a valid restriction of another element declaration particle all of the following must be true: 5 R's declaration's {identity-constraint definitions} is a subset of B's declaration's {identity-constraint definitions}, if any." The issues are: the spec should be clarified to state what "subset" means the subset requirement runs the wrong way -- the derived element's IC's should be a _super_set of the base's. an element decl in a restriction can't have the same ICs as its corresponding decl in the base, because that would violate the named-components-are-unique constraint The original questions were posted to the schema-dev list. Henry summarized the issues in the following mail on schema-comments: http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001OctDec/0187.html and: http://lists.w3.org/Archives/Public/www-xml-schema-comments/2001OctDec/0188.html
See: http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2002Jan/0072.html Resolution: Henry Thompson will create an erratum that highlights the current limitations (see bullet 3 above). The WG may revisit this issue in a future specification.